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A. M. Hooker

Bio: A. M. Hooker is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Citrate synthase & ATPase. The author has an hindex of 3, co-authored 3 publications receiving 779 citations. Previous affiliations of A. M. Hooker include University of California, Irvine.

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Journal ArticleDOI
TL;DR: It is suggested that cardiac muscle cells require thyroxin for normal growth and enzyme development and that Sx may impair cardiac functional capacity by altering Ca2+ activity of actomyosin ATPase.
Abstract: The effects of thyroid deficiency (Td) and of chemical sympathectomy (Sx) were studied on marker enzymes of energy metabolism in cardiac muscle of neonatal and of adult rats. Td prevented the normal development of neonatal body weight, relative heart mass, and cardiac levels of cytochrome c (-22%), citrate synthase (-27%), phosphofructokinase (-20%) and Mg2+- and Ca2+-ATPase activity of purified myofibrils (-33%, -44%). Exogenous thyroxin replacement restored those parameters studied to normal with the exception that it persistently elevated citrate synthase activity significantly above normal control levels. Responses similar to those of Td neonates occurred when adult rats were similarly treated. Sx produced no consistent effects on respiratory and glycogenolytic marker enzymes, but caused a 20% reduction in Ca2+-ATPase activity of both neonatal and adult cardiac myofibrils. These findings suggest that cardiac muscle cells require thyroxin for normal growth and enzyme development. Also, Sx may impair cardiac functional capacity by altering Ca2+ activity of actomyosin ATPase.

19 citations

Journal ArticleDOI
TL;DR: The correlation of an increase in AM ATPase activity with increasing maximal heart rate in different species is of physiological importance to provide adequate perfusion of the heart during diastole.
Abstract: 1. 1. A study was conducted to determine if actomyosin ATPase (AM) is correlated with cardiac function in three species, rats, dogs, and humans. 2. 2. Mg 2+ stimulated ATPase averaged 0.327 ± 0.031, 0.260 ± 0.026, and 0.180 ± 0.015 and Ca 2+ stimulated activity averaged 0.602 + 0.041, 0.291 + 0.028; and 0.258 + 0.019 μ mol/mg/min for rat, dog and human actomyosin samples. Both Mg 2+ and Ca 2+ ATPase were highly correlated with systolic ejection time ( r = −0.99 and −0.90) and maximum heart rate ( r = 0.95 and 0.98). 3. 3. The correlation of an increase in AM ATPase activity with increasing maximal heart rate in different species is of physiological importance to provide adequate perfusion of the heart during diastole.

3 citations


Cited by
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Journal ArticleDOI
12 Jun 1981-Science
TL;DR: It is suggested that somatomedin-C participates in the growth hormone negative feedback loop with an immediate effect on hypothalamic somatostatin and a delayed effect on the anterior pituitary.
Abstract: Somatomedin-C stimulates somatostatin release to a maximum of 390 percent of basal release during short-term (20-minute) incubation of rat hypothalamus. It has no effect on basal or stimulated growth hormone release from primary cultures of rat adenohypophyseal cells during a 4-hour incubation, but inhibits stimulated release by more that 90 percent after 24 hours. These findings suggest that somatomedin-C participates in the growth hormone negative feedback loop with an immediate effect on hypothalamic somatostatin and a delayed effect on the anterior pituitary.

823 citations

Journal ArticleDOI
30 Oct 1987-Science
TL;DR: The gene for the human platelet alpha 2-adrenergic receptor has been cloned with oligonucleotides corresponding to the partial amino acid sequence of the purified receptor, and two related genes have been identified by low stringency Southern blot analysis.
Abstract: The gene for the human platelet alpha 2-adrenergic receptor has been cloned with oligonucleotides corresponding to the partial amino acid sequence of the purified receptor. The identity of this gene has been confirmed by the binding of alpha 2-adrenergic ligands to the cloned receptor expressed in Xenopus laevis oocytes. The deduced amino acid sequence is most similar to the recently cloned human beta 2- and beta 1-adrenergic receptors; however, similarities to the muscarinic cholinergic receptors are also evident. Two related genes have been identified by low stringency Southern blot analysis. These genes may represent additional alpha 2-adrenergic receptor subtypes.

786 citations

Journal ArticleDOI
03 Jun 1988-Science
TL;DR: The alpha 2 and beta 2 adrenergic receptors, both of which are activated by epinephrine, but which can be differentiated by selective drugs, have opposite effects on the adenylyl cyclase system.
Abstract: The alpha 2 and beta 2 adrenergic receptors, both of which are activated by epinephrine, but which can be differentiated by selective drugs, have opposite effects (inhibitory and stimulatory) on the adenylyl cyclase system. The two receptors are homologous with each other, rhodopsin, and other receptors coupled to guanine nucleotide regulatory proteins and they contain seven hydrophobic domains, which may represent transmembrane spanning segments. The function of specific structural domains of these receptors was determined after construction and expression of a series of chimeric alpha 2-,beta 2-adrenergic receptor genes. The specificity for coupling to the stimulatory guanine nucleotide regulatory protein lies within a region extending from the amino terminus of the fifth hydrophobic domain to the carboxyl terminus of the sixth. Major determinants of alpha 2- and beta 2-adrenergic receptor agonist and antagonist ligand binding specificity are contained within the seventh membrane spanning domain. Chimeric receptors should prove useful for elucidating the structural basis of receptor function.

741 citations

Journal ArticleDOI
TL;DR: A distinct, previously unrecognized receptor named CXCR3-B is described, derived from an alternative splicing of the CX CR3 gene that mediates the angiostatic activity of CxCR3 ligands and also acts as functional receptor for CXCL4.
Abstract: The chemokines CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC regulate lymphocyte chemotaxis, mediate vascular pericyte proliferation, and act as angiostatic agents, thus inhibiting tumor growth. These multiple activities are apparently mediated by a unique G protein-coupled receptor, termed CXCR3. The chemokine CXCL4/PF4 shares several activities with CXCL9, CXCL10, and CXCL11, including a powerful angiostatic effect, but its specific receptor is still unknown. Here, we describe a distinct, previously unrecognized receptor named CXCR3-B, derived from an alternative splicing of the CXCR3 gene that mediates the angiostatic activity of CXCR3 ligands and also acts as functional receptor for CXCL4. Human microvascular endothelial cell line-1 (HMEC-1), transfected with either the known CXCR3 (renamed CXCR3-A) or CXCR3-B, bound CXCL9, CXCL10, and CXCL11, whereas CXCL4 showed high affinity only for CXCR3-B. Overexpression of CXCR3-A induced an increase of survival, whereas overexpression of CXCR3-B dramatically reduced DNA synthesis and up-regulated apoptotic HMEC-1 death through activation of distinct signal transduction pathways. Remarkably, primary cultures of human microvascular endothelial cells, whose growth is inhibited by CXCL9, CXCL10, CXCL11, and CXCL4, expressed CXCR3-B, but not CXCR3-A. Finally, monoclonal antibodies raised to selectively recognize CXCR3-B reacted with endothelial cells from neoplastic tissues, providing evidence that CXCR3-B is also expressed in vivo and may account for the angiostatic effects of CXC chemokines.

677 citations

Journal ArticleDOI
TL;DR: The data support the proposal that enhancement of penile erection by sildenafil in patients with erectile dysfunction involves potentiation of the NO-stimulated cGMP signal mediating relaxation of cavernosal smooth muscle during sexual stimulation.

605 citations