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Contractile activity is required for sarcomeric assembly in phenylephrine-induced cardiac myocyte hypertrophy

Contractile activity is required for sarcomeric assembly in phenylephrine-induced cardiac myocyte... Abstract Agonist-induced hypertrophy of cultured neonatal rat ventricular myocytes (NRVM) has been attributed to biochemical signals generated during receptor activation. However, NRVM hypertrophy can also be induced by spontaneous or electrically stimulated contractile activity in the absence of exogenous neurohormonal stimuli. Using single-cell imaging of fura 2-loaded myocytes, we found that low-density, noncontracting NRVM begin to generate intracellular Ca 2+ concentration (Ca 2+ i ) transients and contractile activity within minutes of exposure to the α 1 -adrenergic agonist phenylephrine (PE; 50 μM). However, NRVM pretreated with verapamil and then stimulated with PE failed to elicit Ca 2+ i transients and beating. We therefore examined whether PE-induced Ca 2+ i transients and contractile activity were required to elicit specific aspects of the hypertrophic phenotype. PE treatment (48–72 h) increased cell size, total protein content, total protein-to-DNA ratio, and myosin heavy chain (MHC) isoenzyme content. PE also stimulated sarcomeric protein assembly and prolonged MHC half-life. However, blockade of voltage-gated L-type Ca 2+ channels with verapamil, diltiazem, or nifedipine (10 μM) blocked PE-induced total protein and MHC accumulation and prevented the time-dependent assembly of myofibrillar proteins into sarcomeres. Inhibition of actin-myosin cross-bridge cycling with 2,3-butanedione monoxime (7.5 mM) also prevented PE-induced total protein and MHC accumulation, indicating that mechanical activity, rather than Ca 2+ i transients per se, was required. In contrast, blockade of Ca 2+ i transients and contractile activity did not prevent the PE-induced increase in cell surface area, activation of the mitogen-activated protein kinases ERK1 and ERK2, or upregulation of atrial natriuretic factor gene expression. Thus contractile activity is required to elicit some but not all aspects of the the hypertrophic phenotype induced by α 1 -adrenergic receptor activation. calcium verapamil signal transduction fura 2 gene expression cytoskeleton Footnotes Address for reprint requests: A. M. Samarel, Loyola University Medical Center, Bldg. 110, Rm. 5222, 2160 South First Ave., Maywood, IL 60153. These studies were supported by National Heart, Lung, and Blood Institute (NHLBI) Grants RO1-HL-34328 and HL-52478 and by gifts to the Cardiovascular Institute from the Nalco Foundation, the Eugene J. and Elsie E. Weyler Endowment for Clinical Cardiology Research, and the Ralph and Marian Falk Trust for Medical Research. D. M. Eble was a recipient of NHLBI National Research Service Award F32-HL-09611 during the time these studies were performed. Copyright © 1998 the American Physiological Society http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AJP - Cell Physiology The American Physiological Society

Contractile activity is required for sarcomeric assembly in phenylephrine-induced cardiac myocyte hypertrophy

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Publisher
The American Physiological Society
Copyright
Copyright © 2010 the American Physiological Society
ISSN
0363-6143
eISSN
1522-1563
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Abstract

Abstract Agonist-induced hypertrophy of cultured neonatal rat ventricular myocytes (NRVM) has been attributed to biochemical signals generated during receptor activation. However, NRVM hypertrophy can also be induced by spontaneous or electrically stimulated contractile activity in the absence of exogenous neurohormonal stimuli. Using single-cell imaging of fura 2-loaded myocytes, we found that low-density, noncontracting NRVM begin to generate intracellular Ca 2+ concentration (Ca 2+ i ) transients and contractile activity within minutes of exposure to the α 1 -adrenergic agonist phenylephrine (PE; 50 μM). However, NRVM pretreated with verapamil and then stimulated with PE failed to elicit Ca 2+ i transients and beating. We therefore examined whether PE-induced Ca 2+ i transients and contractile activity were required to elicit specific aspects of the hypertrophic phenotype. PE treatment (48–72 h) increased cell size, total protein content, total protein-to-DNA ratio, and myosin heavy chain (MHC) isoenzyme content. PE also stimulated sarcomeric protein assembly and prolonged MHC half-life. However, blockade of voltage-gated L-type Ca 2+ channels with verapamil, diltiazem, or nifedipine (10 μM) blocked PE-induced total protein and MHC accumulation and prevented the time-dependent assembly of myofibrillar proteins into sarcomeres. Inhibition of actin-myosin cross-bridge cycling with 2,3-butanedione monoxime (7.5 mM) also prevented PE-induced total protein and MHC accumulation, indicating that mechanical activity, rather than Ca 2+ i transients per se, was required. In contrast, blockade of Ca 2+ i transients and contractile activity did not prevent the PE-induced increase in cell surface area, activation of the mitogen-activated protein kinases ERK1 and ERK2, or upregulation of atrial natriuretic factor gene expression. Thus contractile activity is required to elicit some but not all aspects of the the hypertrophic phenotype induced by α 1 -adrenergic receptor activation. calcium verapamil signal transduction fura 2 gene expression cytoskeleton Footnotes Address for reprint requests: A. M. Samarel, Loyola University Medical Center, Bldg. 110, Rm. 5222, 2160 South First Ave., Maywood, IL 60153. These studies were supported by National Heart, Lung, and Blood Institute (NHLBI) Grants RO1-HL-34328 and HL-52478 and by gifts to the Cardiovascular Institute from the Nalco Foundation, the Eugene J. and Elsie E. Weyler Endowment for Clinical Cardiology Research, and the Ralph and Marian Falk Trust for Medical Research. D. M. Eble was a recipient of NHLBI National Research Service Award F32-HL-09611 during the time these studies were performed. Copyright © 1998 the American Physiological Society

Journal

AJP - Cell Physiology – The American Physiological Society

Published: May 1, 1998

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