Showing papers by "Nagoya University published in 2000"

Review of Particle Physics

Abstract: This biennial Review summarizes much of particle physics. Using data from previous editions., plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors., probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V-ud & V-us, V-cb & V-ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.

The status of the tropical rainfall measuring mission (TRMM) after two years in orbit

Abstract: The Tropical Rainfall Measuring Mission (TRMM) satellite was launched on 27 November 1997, and data from all the instruments first became available approximately 30 days after the launch. Since then, much progress has been made in the calibration of the sensors, the improvement of the rainfall algorithms, and applications of these results to areas such as data assimilation and model initialization. The TRMM Microwave Imager (TMI) calibration has been corrected and verified to account for a small source of radiation leaking into the TMI receiver. The precipitation radar calibration has been adjusted upward slightly (by 0.6 dB Z) to match better the ground reference targets; the visible and infrared sensor calibration remains largely unchanged. Two versions of the TRMM rainfall algorithms are discussed. The at-launch (version 4) algorithms showed differences of 40% when averaged over the global Tropics over 30-day periods. The improvements to the rainfall algorithms that were undertaken after launch are presented, and intercomparisons of these products (version 5) show agreement improving to 24% for global tropical monthly averages. The ground-based radar rainfall product generation is discussed. Quality-control issues have delayed the routine production of these products until the summer of 2000, but comparisons of TRMM products with early versions of the ground validation products as well as with rain gauge network data suggest that uncertainties among the TRMM algorithms are of approximately the same magnitude as differences between TRMM products and ground-based rainfall estimates. The TRMM field experiment program is discussed to describe active areas of measurements and plans to use these data for further algorithm improvements. In addition to the many papers in this special issue, results coming from the analysis of TRMM products to study the diurnal cycle, the climatological description of the vertical profile of precipitation, storm types, and the distribution of shallow convection, as well as advances in data assimilation of moisture and model forecast improvements using TRMM data, are discussed in a companion TRMM special issue in the Journal of Climate (1 December 2000, Vol. 13, No. 23).

Development of a digital image database for chest radiographs with and without a lung nodule: receiver operating characteristic analysis of radiologists' detection of pulmonary nodules.

Abstract: OBJECTIVE. We developed a digital image database (www.macnet.or.jp/jsrt2/cdrom_nodules.html) of 247 chest radiographs with and without a lung nodule. The aim of this study was to investigate the characteristics of image databases for potential use in various digital image research projects. Radiologists' detection of solitary pulmonary nodules included in the database was evaluated using a receiver operating characteristic (ROC) analysis.MATERIALS AND METHODS. One hundred and fifty-four conventional chest radiographs with a lung nodule and 93 radiographs without a nodule were selected from 14 medical centers and were digitized by a laser digitizer with a 2048 × 2048 matrix size (0.175-mm pixels) and a 12-bit gray scale. Lung nodule images were classified into five groups according to the degrees of subtlety shown. The observations of 20 participating radiologists were subjected to ROC analysis for detecting solitary pulmonary nodules. Experimental results (areas under the curve, Az) obtained from observer...

Polymorphisms of UDP-Glucuronosyltransferase Gene and Irinotecan Toxicity: A Pharmacogenetic Analysis

Abstract: Irinotecan unexpectedly causes severe toxicity of leukopenia or diarrhea. Irinotecan is metabolized to form active SN-38, which is further conjugated and detoxified by UDP-glucuronosyltransferase (UGT) 1A1 enzyme. Genetic polymorphisms of the UGT1A1 would affect an interindividual variation of the toxicity by irinotecan via the alternation of bioavailability of SN-38. In this case-control study, retrospective review of clinical records and determination of UGT1A1 polymorphisms were performed to investigate whether a patient with the variant UGT1A1 genotypes would be at higher risk for severe toxicity by irinotecan. All patients previously received irinotecan against cancer in university hospitals, cancer centers, or large urban hospitals in Japan. We identified 26 patients who experienced severe toxicity and 92 patients who did not. The relationship was studied between the multiple variant genotypes (UGT1A1*28 in the promoter and UGT1A1*6, UGT1A1*27, UGT1A1*29, and UGT1A1*7 in the coding region) and the severe toxicity of grade 4 leukopenia (< or =0.9 x 10(9)/liter) and/or grade 3 (watery for 5 days or more) or grade 4 (hemorrhagic or dehydration) diarrhea. Of the 26 patients with the severe toxicity, the genotypes of UGT1A1*28 were homozygous in 4 (15%) and heterozygous in 8 (31%), whereas 3 (3%) homozygous and 10 (11%) heterozygous were found among the 92 patients without the severe toxicity. Multivariate analysis suggested that the genotype either heterozygous or homozygous for UGT1A1*28 would be a significant risk factor for severe toxicity by irinotecan (P < 0.001; odds ratio, 7.23; 95% confidence interval, 2.52-22.3). All 3 patients heterozygous for UGT1A1*27 encountered severe toxicity. No statistical association of UGT1A1*6 with the occurrence of severe toxicity was observed. None had UGT1A1*29 or UGT1A1*7. We suggest that determination of the UGT1A1 genotypes might be clinically useful for predicting severe toxicity by irinotecan in cancer patients. This research warrants a prospective trial to corroborate the usefulness of gene diagnosis of UGT1A1 polymorphisms prior tb irinotecan chemotherapy.

Tunnelling effects on surface bound states in unconventional superconductors

Abstract: Recent studies on high-Tc superconductors have aroused new interest in tunnelling effects in unconventional superconductors. Unlike in conventional s-wave superconductors, the d-wave pairing state in these materials has an internal phase of the pair potential. The internal phase as a function of the wavevector of the Cooper pairs has a large influence on the electric properties of tunnelling junctions. Important effects of the internal phase on the Josephson current were first predicted theoretically. The idea has been established through several experiments using high-Tc Josephson junctions, which detect ?-phase shift between the a- and b-axis directions and fractional flux quanta. These results give convincing evidence for d-wave symmetry in high-Tc superconductors. In addition, the existence of new interference effects in the quasiparticle states near surfaces and boundaries has been suggested through theoretical predictions. Experimentally, a large number of tunnelling spectroscopy data showed zero-bias conductance peaks (ZBCPs), the origin of which cannot be explained in terms of the classical concept that a tunnelling conductance spectrum is a phase-insensitive probe of the electronic states. It is clarified theoretically that the observed ZBCPs reflect the formation of zero-energy states on the surface due to the ?-phase shift of internal phase in the d-wave pairing symmetry. The formulation developed for tunnelling spectroscopy suggests that tunnelling spectroscopy is essentially phase sensitive. In addition, the formation of the bound states has been shown to have a serious influence on the electrical properties of Josephson junctions. Several anomalous properties including strong enhancement of the Josephson current in the low-temperature region have been predicted theoretically. In this report, recent developments in tunnelling effects on surface bound states in unconventional superconductors are reviewed.

A low-operating-temperature solid oxide fuel cell in hydrocarbon-Air mixtures

Abstract: The performance of a single-chamber solid oxide fuel cell was studied using a ceria-based solid electrolyte at temperatures below 773 kelvin. Electromotive forces of ∼900 millivolts were generated from the cell in a flowing mixture of ethane or propane and air, where the solid electrolyte functioned as a purely ionic conductor. The electrode-reaction resistance was negligibly small in the total internal resistances of the cell. The resulting peak power density reached 403 and 101 milliwatts per square centimeter at 773 and 623 kelvin, respectively.

The sinoatrial node, a heterogeneous pacemaker structure.

Abstract: This article focuses on the regional heterogeneity of the mammalian sinoatrial (SA) node in terms of cell morphology, pacemaker activity, action potential configuration and conduction, densities of ionic currents (i(Na), i(Ca,L), i(to), i(K,r), i(K,s) and i(f)), expression of gap junction proteins (Cx40, Cx43 and Cx45), autonomic regulation, and ageing. Experimental studies on the single SA node cell to the whole animal are reviewed. The heterogeneity is considered in terms of the gradient model of the SA node, in which there is gradual change in the intrinsic properties of SA node cells from periphery to centre, and the alternative mosaic model, in which there is a variable mix of atrial and SA node cells from periphery to centre. The heterogeneity is important for the dependable functioning of the SA node as the pacemaker for the heart, because (i) via multiple mechanisms, it allows the SA node to drive the surrounding atrial muscle without being suppressed electrotonically; (ii) via an action potential duration gradient and a conduction block zone, it promotes antegrade propagation of excitation from the SA node to the right atrium and prevents reentry of excitation; and (iii) via pacemaker shift, it allows pacemaking to continue under diverse pathophysiological circumstances.

Loss of function of a rice brassinosteroid insensitive1 homolog prevents internode elongation and bending of the lamina joint.

Abstract: Brassinosteroids (BRs) are plant growth–promoting natural products required for plant growth and development. Physiological studies have demonstrated that exogenous BR, alone or in combination with auxin, enhance bending of the lamina joint of rice. However, little is known about the function of endogenous BR in rice or other grass species. We report here the phenotypical and molecular characterization of a rice dwarf mutant, d61, that is less sensitive to BR compared to the wild type. We cloned a rice gene, OsBRI1, with extensive sequence similarity to that of the Arabidopsis BRI gene, which encodes a putative BR receptor kinase. Linkage analysis showed that the OsBRI1 gene is closely linked to the d61 locus. Single nucleotide substitutions found at different sites of the d61 alleles would give rise to amino acid changes in the corresponding polypeptides. Furthermore, introduction of the entire OsBRI1 coding region, including the 5′ and 3′ flanking sequences, into d61 plants complemented the mutation to display the wild-type phenotype. Transgenic plants carrying the antisense strand of the OsBRI1 transcript showed similar or even more severe phenotypes than those of the d61 mutants. Our results show that OsBRI1 functions in various growth and developmental processes in rice, including (1) internode elongation, by inducing the formation of the intercalary meristem and the longitudinal elongation of internode cells; (2) bending of the lamina joint; and (3) skotomorphogenesis.

Regulation of C. elegans life-span by insulinlike signaling in the nervous system.

Abstract: An insulinlike signaling pathway controls Caenorhabditis elegans aging, metabolism, and development. Mutations in the daf-2 insulin receptor-like gene or the downstream age-1 phosphoinositide 3-kinase gene extend adult life-span by two- to threefold. To identify tissues where this pathway regulates aging and metabolism, we restored daf-2 pathway signaling to only neurons, muscle, or intestine. Insulinlike signaling in neurons alone was sufficient to specify wild-type life-span, but muscle or intestinal signaling was not. However, restoring daf-2 pathway signaling to muscle rescued metabolic defects, thus decoupling regulation of life-span and metabolism. These findings point to the nervous system as a central regulator of animal longevity.

Physiology of Reproduction

Abstract: Publisher Summary The rat is the most popular experiment animal for studying reproductive physiology. Investigations have found that they have much shorter reproductive cycles compared with larger animals. Stages such as puberty, the estrous cycle, pregnancy, and lactation are all much shorter. In addition, rats display various types of estrous cycle, such as estrous cycle with luteal phase or spontaneous ovulation, when they receive certain stimuli. Rat sexual behavior also plays a significant role in the field of research. In order to observe sexual behavior in rats, a male rat that has already been trained to mate with normal females several times is placed in a test cage under a red dim light, e.g. a 60 x 50 x 40 cm plastic cage with bedding at the bottom to facilitate activity. After several minutes, a steroid-induced estrous female is introduced. The male starts an investigation and genital sniffing if he realizes that the female is in estrus. The male then shows mounting behavior with a pelvic thrust. After ejaculation, the male suddenly quits frequent pelvic thrusts and leaves the female. The female shows the lordosis behavior in response to the male mounting her.

CREB-binding protein sequestration by expanded polyglutamine

Abstract: Spinal and bulbar muscular atrophy (SBMA) is one of eight inherited neurodegenerative diseases known to be caused by CAG repeat expansion The expansion results in an expanded polyglutamine tract, which likely confers a novel, toxic function to the affected protein Cell culture and transgenic mouse studies have implicated the nucleus as a site for pathogenesis, suggesting that a critical nuclear factor or process is disrupted by the polyglutamine expansion In this report we present evidence that CREB-binding protein (CBP), a transcriptional co-activator that orchestrates nuclear response to a variety of cell signaling cascades, is incorporated into nuclear inclusions formed by polyglutamine-containing proteins in cultured cells, transgenic mice and tissue from patients with SBMA We also show CBP incorporation into nuclear inclusions formed in a cell culture model of another polyglutamine disease, spinocerebellar ataxia type 3 We present evidence that soluble levels of CBP are reduced in cells expressing expanded polyglutamine despite increased levels of CBP mRNA Finally, we demonstrate that over-expression of CBP rescues cells from polyglutamine-mediated toxicity in neuronal cell culture These data support a CBP-sequestration model of polyglutamine expansion disease

Tandem-duplicated Flt3 constitutively activates STAT5 and MAP kinase and introduces autonomous cell growth in IL-3-dependent cell lines.

Abstract: We have recently identified an internal tandem duplication of the human Flt3 gene in approximately 20% of acute myeloid leukemia (AML) cases. In the present study, the wild-type and the mutant Flt3 genes were transfected into two IL-3-dependent cell lines, 32D and BA/F3 cells. Mutant Flt3-transfected cells exhibited autonomous growth while wild-type Flt3-transfected cells with the continuous stimulation of Flt3 ligand exhibited a minimal proliferation. Cells expressing mutant Flt3 showed constitutive activation of STAT5 and MAP kinase. In contrast, Flt3 ligand stimulation caused rapid activation of MAP kinase but not STAT5 in cells expressing wild-type Flt3. Finally, we found constitutive activation of MAP kinase and STAT5 in all clinical samples of AML patients with mutant Flt3. Our study shows the significance of internal tandem duplication of Flt3 receptors for leukemia cell expansion.

Involvement of Brain-Derived Neurotrophic Factor in Spatial Memory Formation and Maintenance in a Radial Arm Maze Test in Rats

Abstract: Brain-derived neurotrophic factor (BDNF) regulates both short-term synaptic functions and activity-dependent synaptic plasticity such as long-term potentiation In the present study, we investigated the role of BDNF in the spatial reference and working memory in a radial arm maze test The radial arm maze training resulted in a significant increase in the BDNF mRNA expression in the hippocampus, although the expression in the frontal cortex did not change When spatial learning was inhibited by treatment with 7-nitroindazole, an inhibitor of brain nitric oxide synthase, the increase in the hippocampal BDNF mRNA did not occur To clarify the causal relation between BDNF mRNA expression and spatial memory formation, we examined the effects of antisense BDNF treatment on spatial learning and memory A continuous intracerebroventricular infusion of antisense BDNF oligonucleotide resulted in an impairment of spatial learning, although the sense oligonucleotide had no effect Treatment with antisense, but not sense, BDNF oligonucleotide was associated with a significant reduction of BDNF mRNA and protein levels in the hippocampus Furthermore, treatment with antisense BDNF oligonucleotide in rats, which had previously acquired spatial memory by an extensive training, impaired both reference and working memory There were no differences in locomotor activity, food consumption, and body weight between the antisense and sense oligonucleotide-treated rats These results suggest that BDNF plays an important role not only in the formation, but also in the retention and/or recall, of spatial memory

C66 fullerene encaging a scandium dimer

Abstract: The geometry of carbon cages (fullerenes) is governed by the isolated-pentagon rule (IPR)1,2, which states that the most stable fullerenes are those in which all pentagons are surrounded by five hexagons. Although this rule has been verified experimentally3,4,5, it is impossible for fullerenes in the range C60 to C70 to obey it. Here we describe the production and characterization of an IPR-violating metallofullerene, Sc2@C66, a C66 fullerene encaging a scandium dimer. Our results indicate that encapsulation of the metal dimer significantly stabilizes this otherwise extremely unstable C66 fullerene.

An Oxide Single Crystal with High Thermoelectric Performance in Air

Abstract: An oxide single-crystalline whisker with high thermoelectric properties at temperatures (T) higher than 600 K in air has been discovered. This whisker is assigned to Ca2Co2O5 phase (abbreviated to Co-225 whiskers) and has a layered structure in which Co–O layers of two different kinds alternate in the direction of the c-axis. Seebeck coefficient of the whiskers is higher than 100 µVK-1 at 100 K and increases with temperature up to 210 µVK-1. Temperature dependence of electric resistivity shows a semiconducting-like behavior. These results indicate that the electric carriers are transported via hopping conduction. Using thermal conductivity of a Co-225 polycrystalline sample, figure of merit (ZT) of the Co-225 whiskers is estimated 1.2–2.7 at T≥873 K. This compound is characterized with regard to low mobility and high density of carriers, which contradicts the conventional materials with high thermoelectric properties.

One-dimensional metallofullerene crystal generated inside single-walled carbon nanotubes.

Abstract: Electron microscope imaging for gadolinium metallofullerenes encapsulating in single-wall carbon nanotubes [(Gd@C82)n@SWNTs] identifies the single Gd atom encaged in each. The intermolecular distance between Gd@C82 is extremely regular, regarding the chains of Gd@C82 as novel one-dimensional crystals. Chemical state analysis of Gd atoms suggests evidence for charge transfer from Gd to either a fullerene cage or a nanotube. The slopes of the temperature dependence of electric resistance for the mat-like films of (Gd@C82)n@SWNTs and (C60)n@SWNTs are much steeper than that for empty SWNTs, suggesting the electron scattering due to the electrostatic potential from inside fullerenes playing an important role.

The Arabidopsis HKT1 Gene Homolog Mediates Inward Na+ Currents in Xenopus laevis Oocytes and Na+ Uptake in Saccharomyces cerevisiae

Abstract: The Na + -K + co-transporter HKT1, first isolated from wheat, mediates high-affinity K + uptake. The function of HKT1 in plants, however, remains to be elucidated, and the isolation of HKT1 homologs from Arabidopsis would further studies of the roles of HKT1 genes in plants. We report here the isolation of a cDNA homologous to HKT1 from Arabidopsis ( AtHKT1 ) and the characterization of its mode of ion transport in heterologous systems. The deduced amino acid sequence of AtHKT1 is 41% identical to that of HKT1, and the hydropathy profiles are very similar. AtHKT1 is expressed in roots and, to a lesser extent, in other tissues. Interestingly, we found that the ion transport properties of AtHKT1 are significantly different from the wheat counterpart. As detected by electrophysiological measurements, AtHKT1 functioned as a selective Na + uptake transporter in Xenopus laevis oocytes, and the presence of external K + did not affect the AtHKT1-mediated ion conductance (unlike that of HKT1). When expressed in Saccharomyces cerevisiae , AtHKT1 inhibited growth of the yeast in a medium containing high levels of Na + , which correlates to the large inward Na + currents found in the oocytes. Furthermore, in contrast to HKT1, AtHKT1 did not complement the growth of yeast cells deficient in K + uptake when cultured in K + -limiting medium. However, expression of AtHKT1 did rescue Escherichia coli mutants carrying deletions in K + transporters. The rescue was associated with a less than 2-fold stimulation of K + uptake into K + -depleted cells. These data demonstrate that AtHKT1 differs in its transport properties from the wheat HKT1, and that AtHKT1 can mediate Na + and, to a small degree, K + transport in heterologous expression systems.

Circadian waves of expression of the APRR1/TOC1 family of pseudo-response regulators in Arabidopsis thaliana: insight into the plant circadian clock.

Abstract: The Arabidopsis pseudo-response regulator, APRR1, has a unique structural design containing a pseudo-receiver domain and a C-terminal CONSTANS motif. This protein was originally characterized as a presumed component of the His-to-Asp phosphorelay systems in Arabidopsis thaliana. Recently, it was reported that APRR1 is identical to the TOC1 gene product, a mutational lesion of which affects the periods of many circadian rhythms in Arabidopsis plants. TOC1 is believed to be a component of the presumed circadian clock (or central oscillator). Based on these facts, in this study four more genes, each encoding a member of the APRR1/TOC1 family of pseudo-response regulators were identified and characterized with special reference to circadian rhythms. It was found that all these members of the APRR1/TOC1 family (APRR1, APRR3, APRR5, APRR7, and APRR9) are subjected to a circadian rhythm at the level of transcription. Furthermore, in a given 24 h period, the APRR-mRNAs started accumulating sequentially after dawn with 2-3 h intervals in the order of APRR9-->APRR7-->APRR5-->APRR3-->APRR1. These sequential events of transcription, termed 'circadian waves of APRR1/TOCI', were not significantly affected by the photoperiod conditions, if any (e.g. both long and short days), and the expression of APRR9 was first boosted always after dawn. Among these APRRs, in fact, only the expression of APRR9 was rapidly and transiently induced also by white light, whereas such light responses of others were very dull, if any. These results collectively support the view that these members of the APRR1/TOC1 family are together all involved in an as yet unknown mechanism underlying the Arabidopsis circadian clock. Here we propose that the circadian waves of the APRR1/TOC1 family members are most likely a molecular basis of such a biological clock in higher plants.

Aggressive preoperative management and extended surgery for hilar cholangiocarcinoma: Nagoya experience.

Abstract: From 1977 to 1997, surgical resection was possible in 142 (80%) of 177 patients with hilar cholangiocarcinoma after relieving jaundice by single or multiple percutaneous transhepatic biliary drainage followed by percutaneous transhepatic cholangioscopy and/or percutaneous trans-hepatic portal vein embolization. Curative resection was possible in 108 (61%) of the 142 patients, and 100 of these patients underwent various types of hepatectomy with caudate lobectomy for a 30-day operative mortality rate of 6% and 9% hospital mortality. Combined portal vein resection was carried out in 43 cases including 41 hepatectomies and 2 bile duct resections. Hepatopancreatoduodenectomy was performed in 16 patients. Cancer recurrence was observed in 58 of the 108 patients undergoing curative resection. The 3-, 5-, and 10-year survival rates for 100 patients undergoing curative hepatectomy and 8 with curative bile duct resection were 43%, 26%, and 19%; and 31%, 16%, and 0%, respectively; those for 40 patients with positive lymph node metastasis, 84 with perineural invasion, and 43 with combined portal vein resection were 27%, 14%, and 7%; 34%, 21%, and 13%; and 18%, 6%, and 0%, respectively. These survival rates are significantly better than those for 35 patients with unresectable cancer. Curative resection after aggressive preoperative management is recommended as a reasonable surgical approach to hilar cholangiocarcinoma.

Enhanced tolerance to salt stress in transgenic rice that overexpresses chloroplast glutamine synthetase.

Abstract: The potential role of photorespiration in the protection against salt stress was examined with transgenic rice plants. Oryza sativa L. cv. Kinuhikari was transformed with a chloroplastic glutamine synthetase (GS2) gene from rice. Each transgenic rice plant line showed a different accumulation level of GS2. A transgenic plant line, G39-2, which accumulated about 1.5-fold more GS2 than the control plant, had an increased photorespiration capacity. In another line, G241-12, GS2 was almost lost and photorespiration activity could not be detected. Fluorescence quenching analysis revealed that photorespiration could prevent the over-reduction of electron transport systems. When exposed to 150 mM NaCl for 2 weeks, the control rice plants completely lost photosystem II activity, but G39-2 plants retained more than 90% activity after the 2-week treatment, whereas G241-12 plants lost these activities within one week. In the presence of isonicotinic acid hydrazide, an inhibitor of photorespiration, G39-2 showed the same salt tolerance as the control plants. The intracellular contents of NH4 + and Na+ in the stressed plants correlated well with the levels of GS2. Thus, the enhancement of photorespiration conferred resistance to salt in rice plants. Preliminary results suggest chilling tolerance in the transformant.

Mathematical models of action potentials in the periphery and center of the rabbit sinoatrial node

Abstract: Mathematical models of the action potential in the periphery and center of the rabbit sinoatrial (SA) node have been developed on the basis of published experimental data. Simulated action potentials are consistent with those recorded experimentally: the model-generated peripheral action potential has a more negative takeoff potential, faster upstroke, more positive peak value, prominent phase 1 repolarization, greater amplitude, shorter duration, and more negative maximum diastolic potential than the model-generated central action potential. In addition, the model peripheral cell shows faster pacemaking. The models behave qualitatively the same as tissue from the periphery and center of the SA node in response to block of tetrodotoxin-sensitive Na(+) current, L- and T-type Ca(2+) currents, 4-aminopyridine-sensitive transient outward current, rapid and slow delayed rectifying K(+) currents, and hyperpolarization-activated current. A one-dimensional model of a string of SA node tissue, incorporating regional heterogeneity, coupled to a string of atrial tissue has been constructed to simulate the behavior of the intact SA node. In the one-dimensional model, the spontaneous action potential initiated in the center propagates to the periphery at approximately 0.06 m/s and then into the atrial muscle at 0.62 m/s.