Showing papers by "University of Maryland, Baltimore published in 1970"

Equilibrium and kinetic properties of the interaction between tetrodotoxin and the excitable membrane of the squid giant axon.

Abstract: Squid giant axons were treated with tetrodotoxin (TTX) in concentrations ranging from 1 nM to 25 nM and the resulting decrease in sodium current was followed in time using the voltage clamp technique. The removal of TTX from the bathing solution produced only partial recovery of the sodium current. This suggests that the over-all interaction is more complex than just a reversible reaction. By correcting for the partial irreversibility of the decrease in sodium current, a dissociation constant of 3.31 x 10(-9)M was calculated for the reaction between TTX and the reactive site of the membrane. The data obtained fit a dose-response curve modified to incorporate the correction for partial irreversibility when calculated for a one-to-one stoichiometry. The fit disagreed with that calculated for a reaction between two molecules of TTX with a single membrane-reactive site, but neither supported nor disproved the possibility of a complex formed by two reactive sites with one molecule of TTX. Values of the rate constants for the formation and dissociation of the TTX-membrane complex, k(1) and k(2), respectively, were obtained from the kinetic data. The values are: k(1) = 0.202 x 10(8)M(-1), and k(2) = 0.116 min(-1). The magnitude of the dissociation constant derived from these values is 5.74 x 10(-9)M, which has the same order of magnitude as that obtained from equilibrium measurements. Arrhenius plots of the rate constants gave values for the thermodynamic quantities of activation.

Effects of intracellular adenosine-5'-diphosphate and orthophosphate on the sensitivity of sodium efflux from squid axon to external sodium and potassium.

Abstract: A study was made of sodium efflux from squid giant axon, and its sensitivity to external K and Na. When sodium efflux from untreated axons was strongly stimulated by Ko, Nao was inhibitory; when dependence on Ko was low, Nao had a stimulatory effect. Incipient CN poisoning or apyrase injection, which produces high intracellular levels of ADP1 and Pi, rendered sodium efflux less dependent on external K and more dependent on external Na. Injection of ADP, AMP, arginine, or creatine + creatine phosphokinase, all of which raise ADP levels without raising Pi levels, had the same effect as incipient CN poisoning. Pi injection had no effect on the K sensitivity of sodium efflux. Axons depleted of arginine and phosphoarginine by injection of arginase still lost their K sensitivity when the ATP:ADP ratio was lowered and regained it partially when the ratio was raised. Rough calculations show that sodium efflux is maximally Ko-dependent when the ATP:ADP ratio is about 10:1, becomes insensitive to Ko when the ratio is about 1:2, and is inhibited by Ko when the ratio is about 1:10. Deoxy-ATP mimicked ADP when injected into intact axons. Excess Mg, as well as Pi, inhibited both strophanthidin-sensitive and strophanthidin-insensitive sodium efflux. An outline is presented for a model which might explain the effects of ADP, Pi and deoxy-ATP.

Ultrastructure of a Temperature-Sensitive Rod− Mutant of Bacillus subtilis

Abstract: Mutant 168ts-200B, resulting from nitrosoguanidine treatment of Bacillus subtilis 168 ( trp − C2), exhibits a rod-to-sphere morphogenetic interconversion when the incubation temperature is 30 or 45 C, respectively. Ultrathin sections of rods grown at 30 C, after glutaraldehyde-osmium uranium-lead fixation and staining, show trilaminar cell walls with a well-developed underlying periplasm as in wild-type cells. However, the outer wall layer is irregular, and abnormal protrusions of wall material occur at the cross-walls. In contrast, cells growing at 45 C become rounded and are intersected randomly by irregular cross-walls which fail to split normally, resulting in large spherical masses. In these, the outer and inner wall layers and periplasm are lost, and the wall consists only of irregularly thickened and loosely organized middle layer. Wall ultrastructure is reversible in either direction as cell shape changes during temperature shifts. Mesosomes are rare and atypical at either temperature. It thus appears that cell wall ultrastructure is altered by the conditional (temperature-sensitive) mutation, and that loss of normal wall and submural organization is correlated with changes in cell size and shape as well as with inability to complete cell division. Preliminary studies after transformation of the mutant locus to another strain and growth at 45 C showed an increase in mucopeptide, loss of wall teichoic acid, failure of phage adsorption, and identical ultrastructural changes. The site of expression of the basic defect—be it in wall, submural region, or membrane—is undetermined. Images

Selecting One of Two Treatments When the Responses are Dichotomous

Abstract: A decision theoretic approach to the design of a clinical trial is considered for the situation in which a total of N patients with a disease receive one of two treatments and the responses to the treatments are dichotomous. Two costs are considered: The cost of treating a patient with the inferior treatment and the cost of conducting the trial. Minimax and Bayes procedures are used to determine the optimum size of a fixed sample trial. Bayes solutions for the optimum sample size are given for a variety of beta prior distributions and various values of N. Minimax solutions are given for a variety of regions over which the minimaxing was performed, and for various values of N. The optimum sample sizes are found to be asymptotically proportional to N 1/2 using the Bayes procedure and N 2/3 using the minimax procedure. The consequences of erring in specifying the value of N are explored.

Neuromuscular Contacts in Intracranial Arteries of the Cat

Abstract: Nerves of intracranital arteries of the cat were restricted to adventitia, with neuromuscular contacts observed only at the border of adventitia and media. Axons of such neuromuscular contacts possessed at least two different populations of synaptic vesicles. One axonal type contained manzy small (500 angstroms in diameter) granular vesicles and occasional agranular vesicles. The other contained only agranular vesicles.

Positive and Negative Feedback Effects of Estrogen on Pituitary LH Synthesis and Release in Normal and Androgen-Sterilized Female Rats

Abstract: Changes in pituitary and plasma LH concentrations after ovariectomy alone or in combination with single injections of various dosages of estrogen were evaluated. Investigations were conducted in immature and adult normal and sterile female rats to study changes with age and differences in thresholds of response to estrogen on LH synthesis vs. release. In immature rats (30 days of age) plasma LH was not detectable. Ovariectomy at 20 days of age, with autopsy 10 days later, resulted in an increase in plasma LH to 11.3 μg/100 ml although pituitary LH concentrations remained unaltered. Injection of 0.05 μg estradiol benzoate (EB)/100 g body wt 7 days after ovariectomy (day 27 of age) failed to alter significantly pituitary and plasma LH concentrations. With the injection of 0.1 fig EB/100 g body wt, a significant increase in pituitary LH occurred, while plasma LH concentrations were unaffected. Estrogen injected as 0.5 μg/100 g body wt inhibited LH release although pituitary LH synthesis was not suppressed an...

Partial purification of sea nettle (Chrysaora quinquecirrha) nematocyst toxin.

Abstract: SummarySoluble toxin was released from fresh Chrysaora quinquecirrha (sea nettle) nematocysts by gentle grinding or sonic treatment in distilled water. The lethal activity was not decreased by three cycles of freezing and thawing nor by lyophilization. Organic solvents such as acetone, ether, alcohol, and dimethylsulfoxide inactivated the toxin. Passage of the toxin through Sephadex gel results in partial purification and separation of the lethal activity into at least 2 fractions which are presumably proteinaceous.The authors acknowledge the aid and assistance of Drs. Elijah Adams, Seymour H. Pomerantz, and J. Tyson Tilden of the University of Maryland School of Medicine.

Effects of β-MSH, Cortisol and ACTH on Tyrosinase in the Skin of Newborn Hamsters and Mice

Abstract: Administration of β-melanocyte stimulating hormone (MSH) to newborn Syrian golden hamsters and to black and brown mice increases tyrosinase activity in body skin by 30-50% after 2 to 4 days of daily treatment. The low ventral skin activity in hamsters can be increased over 100% by this treatment. Cortisol treatment lowers tyrosinase activity in both hamsters and mice, and this action is prevented by simultaneous treatment with MSH. ACTH does not lead to consistent increases or decreases in hamster enzyme, but interpretation is hampered because ACTH administration probably increases endogenous glucocorticoid production. Prolactin, growth hormone, luteinizing hormone and thyroid stimulating hormone have no significant effect on hamster tyrosinase. It seems likely that conditions in man and other mammals that result in elevated levels of MSH are associated with increases in skin tyrosinase and that the increased enzyme produces the dark skin or hair pigmentation. Cortisol may lower tyrosinase by blocking rel...

Laminar Air Purge of Microorganisms in Dental Aerosols: Prophylactic Procedures with the Ultrasonic Scaler

Abstract: Studies of 50 patients undergoing prophylaxis in a dental operatory equipped with laminar airflow showed that from more than 40,400 viable particles containing one or more microbes collected from dental aerosols, about 40,267 were recovered when laminar air was not in use. Airborne contamination reductions of 99.7% were effected in the dental office when a vertical downflow of laminar, high efj"zcieney particulate filtered air was present.

Treatment of Falciparum Malaria Caused by Strain Resistant to Quinine

Abstract: Malaria caused by the Vietnam (Smith) strain of Plasmodium falciparum, isolated from a patient in the United States in 1969, is insusceptible to treatment with chloroquine phosphate, pyrimethamine, and chloroguanide hydrochloride. Radical cure has been obtained in some infected nonimmune patients by the use of quinine in courses of 8.1 gm (base) or more, but in other patients the infection has recrudesced following 22.7 gm (base) given over 14 days; in one patient despite demonstrated normal absorption the latter treatment failed to produce improvement, while addition of pyrimethamine in another did not clear parasitemia. Radical cure was achieved in an average time of 3 days in all of seven men receiving 18.9 gm (base) of quinine over 14 days (1.66 gm of quinine sulfate each day), with 1.0 gm of sulfalene given in four divided doses on the first day .

Mucopolysaccharides in odontogenesis. Histochemical and autoradiographic study.

Abstract: Localization of sulfomucopolysaccharides in developing teeth of Swiss albino mice was detected by S35 autoradiography and histochemistry. A positive correlation was found to exist between autoradiographic and histochemical data with regard to the localization of sulfomucopolysaccharides. Autoradiography, however, revealed some sites of localization which were not detectable by histochemistry, namely, the odontoblasts and stratum intermedium. Fetuses which received the isotope via maternal injection at the cap stage of tooth development and were sacrificed after 2 hours of isotope action displayed rapid incorporation of the isotope in the components of the dental papilla. In the enamel organ, however, only moderate activity was recorded. When the time interval between injection and sacrifice of the experimental animals was increased to 20 hours, intense activity was observed in the enamel organ. With progressively longer intervals between injection and sacrifice, S35 was demonstrable first in odontoblasts and later in the predentin. This occurred as a band or active zone which migrated toward the dentino-enamel junction. With the increasing intervals between injection and sacrifice, first the odontoblasts were active, then predentin was active while the odontoblasts became reduced in activity, after which the dentin matrix gained activity while the predentin decreased somewhat in activity. This pattern is consistent with appositional growth. A linear band of activity was not observed in the enamel matrix; rather, the activity was present as a diffuse stippling over a relatively large area of the matrix. The sulfomucopolysaccharide which existed in dentin matrix was postulated to have originated from the cells of both the odontoblastic layer and the dental papilla.

Renal hilar lymph. Effects of diuresis on flow and composition in dogs.

Abstract: Renal lymph was collected from single hilar lymphatics in 58 anesthetized dogs (1) to study the mechanism by which lymph production is affected during diuresis and (2) to determine whether a medullary contribution to renal lymph could be defined by changes in the electrolyte concentration of hilar lymph with concomitant alterations in the concentration gradient of the renal medulla. When diuresis was induced by a solute load (mannitol), lymph flow increased by 25 to 300%. On the other hand, when diuresis was induced without such a solute load, lymph flow was either unaffected (mersalyl) or slightly reduced (furosemide). It was concluded that the effect of mannitol on renal lymph flow was mediated primarily through its general effect on extracellular fluid rather than through any specific intrarenal consequence of the diuresis itself. Control hilar lymph-to-plasma concentration ratios for Na+ (1.057 ± 0.040), Cl- (1.129 ± 0.040) and Ca2+ (0.770 ± 0.046) but not K+ (0.0986 ± 0.086) were found to be significantly different from 1.0. Failure of mannitol diuresis to alter significantly the lymph-plasma ratios of Na+ and Cl- provided evidence that the high electrolyte concentrations of the inner medulla were not reflected in hilar lymph. The finding that furosemide abolished the lymph-plasma concentration difference for Na+ and significantly reduced that for Cl- was taken as evidence that the outer medulla was a significant source of renal hilar lymph.

Enzymatic fluorometric determination of acetylcholine in biological extracts.

Abstract: — Acetylcholine was determined fluorometrically by the following enzymic reactions: (1) ACh = Acetate + Choline (2) Acetate + ATP + CoASH = Acetyl-SCoA + AMP + PPi (3) Malate + NAD+= Oxalacetate + NADH (4) Oxalacetate + Acetyl-SCoA = CoASH + Citrate The fluorescence produced by NADH was stoichiometric with the ACh present and the citrate formed. The complete system contained acetylcholinesterase (EC 3.1.1.7), acetyl-CoA synthetase (EC 6.2.1.1), malate dehydrogenase (EC 1.1.1.37), and citrate condensing enzyme (EC 4.1.3.7). The acetyl-CoA synthetase was rate limiting in the system. Authentic samples of ACh (10−8 to 10−9mol) were measured with ±5 per cent reproducibility; this corresponds to the content of an 80 mg (fresh weight) sample of brain. Tissue levels of ACh in this concentration range, within normal biological variation, were determined with ±15 per cent reproducibility. The method can also be employed to measure acetate and acetyl-SCoA with the same degrees of sensitivity and reproducibility. The method can be used to measure ‘total’ and ‘bound’ ACh and thus to estimate ‘free’ ACh, by varying the extraction procedure. Values obtained in the manner described agree with those previously reported in the literature. Troublesome fluorescence in brain extracts was effectively removed with acid-washed Florisil.

Evaluation of a school for young mothers. The frequency of prematurity among infants born to mothers under 17 years of age, according to the mother's attendance of a special school during pregnancy.

Abstract: Registration with a social agency, required attendance of prenatal care, a school lunch, supplemental milk, counseling, nutritional education, health education, group discussion, and selfgovernment are elements of a public school program for teen-age mothers. To study the health impact of this program, we located the birth certificates of children born to mothers who were 16 years of age and under and who attended the program. We matched these certificates with certificates of children of the same race and sex born to mothers of the same age living in similar socioeconomic census tracts who did not attend the school but who gave birth during the same period of time. This gave us a study and control group totaling 448 births to mothers 14, 15, and 16 years old. We defined low birth weight as under 2,501 gm and found 23.7% of the control group and 11.6% of the study group to be low birth weight infants. We defined gestation periods less than 37 weeks as premature and found 34.4% of the control group and 21.4% of the study group to be born prematurely. Both of these differences were statistically significant at the level of p smaller than .01. The slightly diminished frequency of prenatal care in the control group was not significantly associated with the differences in birth weight or gestational age. One infant died in the study group and eight infants died in the control group. The differences between the study group and the control group were most pronounced among the 14-year-old mothers.

How Social Workers Perceive Lawyers

Abstract: Development of programs to make legal services available to social work clients requires that social workers learn to identify a need for legal consultation

Properties of the Inducible Hydroxyproline Transport System of Pseudomonas putida

Abstract: Features of the transport system for hydroxyproline in a strain of Pseudomonas putida were studied A mutant, lacking hydroxyproline-2 epimerase and unable to metabolize hydroxy-l-proline, was shown to transport and accumulate this compound after induction Both entry and exit rates were examined, and kinetic constants for the reaction were determined Increasing the induction time from 05 to 3 hr increased the entry rate three- to fourfold but had only a small and variable effect on the exit rate Entry followed saturation kinetics For hydroxy-l-proline, the Km and Vmax values were found to be 3 × 10−5m and 6 μmoles per g (dry weight) per min, respectively The Km and Vmax for the epimer allohydroxy-d-proline were 10−3m and 01 μmole per g (dry weight) per min Entry rates into “loaded” and “unloaded” cells were found to be the same Exit was shown to be first order over the range of internal substrate concentrations measured Exit rates were measured by several different methods and found to be independent of external substrate concentration The first-order exit rate constant was computed to be 023 min−1 Several metabolic inhibitors were examined for their effect on transport The inhibitory action of N-ethyl maleimide was shown to be greatly reduced if cells were allowed to accumulate hydroxy-l-proline before exposure to the inhibitor A number of other amino acids interfered with the transport of hydroxy-l-proline; the greatest effect was produced by l-alanine and l-proline