Modulation of contractile protein synthesis by agents that alter calcium flux

J Mol Cell Cardiol 24 (Supplement

III) (1992)

P70 Cathy J. B&Ii& and Howard E. Morgan. Weis Center for Research, Geisinger Clinic, Danville, PA 17822 USA. Although cardiac hyperlrophy has been extensively investigated, the mechanisms initiating cardiac cellular growth are unknown. The neonatal pig heart provides a unique and attractive model in which to study cardiac growth because the more slowly-growing right ventricle (RV) provides an intmorgan control for the rapidly-growing left ventricle (LV) to account for variability in animal size and nutritional states. In this study, we have used enalapril maleatc-treated piglets to investigate. the potential role of angiotensin II (AII) and a-adrenergic receptor stimulation in modulating cardiac growth. We have previously shown that pre-treatment of piglets with enalapril @g/d x 3d) results in reduced growth of the LV. In addition, pre-treatment of piglets with this drug reduced the rate of ribosome formation and protein synthesis in the LV as measured by incorporation of [3H] phenylalanine during heart perfusion Addition of 1pM AI1 to the perfbsate was ineffective in restoring rates of ribosome formation or protein synthesis to that observed in hearts from untreated piglets. This indicates that AI1 does not have a direct effect on ribosome formation and protein synthesis in the neonatal pig heart or that the time comse required for activation of this pathway is longer than can be observed in the isolated perfused heart. Addition of 1,&i norepinephrine and 1,uM propranolol to the perfosate increased the rate of ribosome formation in the LV (1269268 vs X587+81 moo1 Phe/g protein h) with no change in the RV (1075~45 vs 1160?50 mu01 Phe/g protein h). The rate of total protein synthesis was unchanged by norepinephrine and propranolol in either ventricle. Similarly, the addition of 1pM phenylcphrine and 1,uM propranolol to the perfusate increased rates of ribosome formation in the LV with no change in the RV. The presence of prazosin (lOOaM) in the perfusate blocked the stimulatory effect of either norepinepbrine or phenylephrine on rlbosome formation in the LV. These results suggest a potential role for a-adrenergic receptor stimulation in cardiac growth in the newborn piglet heart.

P71

P-ADRENERGIC MYOCYTE

STIMULATION GROWTH FACTOR

OF CARDIAC PRODUCTION

NON-MYOCYTES

INCREASES

NON-

Carlin S. Long, Wend Hartogensis, Megan Cony, and Paul C. Simpson. Division of Cardiology, San Francisco VA Medic 9 Center, San Francisco, CA 94121. Although their action has been presumed to result from direct effects on the cardiac muscle cells (MCs), little work has been done addressing the effects of catecholamines on the supporting non-myocytes (NMCs) of the heart We have recently identified medium conditioned by neonatal NMCs fNMC-CM) as the source of a growth-promoting factor which leads to cardiac MC hypertmphy in culture. Since cardiac NMCs also contain adrenergic receptors (both a and p) on their cell surface, we asked whether adrenergic stimulation of these NMCs could stimulate MC growth. While Isoproterenol (ISO, 0.2@vI) caused no increase in the per cell contents of total protein in the NMCs, inclusion of IS0 in the medium used in the production of NMC-CM augmented the growth promoting effects of this NMC-CM by more than 60%. This increase was not seen with the al agonist Phenylephrine suggesting that this effect is specific to the p adrenergic receptor. TGFp3 is unique in the family of growth factors in that it contains an upstream CAMP Response Element. NMCs were treated with IS0 over 48 hours and TGFpl and TGFP3 mRNA analyzed by Northern analysis. Treatment with IS0 increased steady state mRNA levels for TGFp3 but not that for the closely related TGFpl over this time period We believe that this is the fit report indicating that a potential mechanism for the observed effects of p adrenergic stimulation on myocardial cellsin culture and possibly relevant in vivo is the contribution of p stimulated factor(s) produced by NMCs which act in a paracrine fashion on myocardial cells.

P72

MODULATION CiLCkJM

OF

CONTRACTILE

PROTEIN

SYNTHESIS

BY

AGENTS

THAT

ALTER

FLUX.

Robert S. Decker, Melissa Cl. Cook, Marlene L. Decker and William A. Clark. Deptartment of Medicine, Northwestern University Medical School, Chicago, IL 60611, USA. . . .. p-adrenergic agonists promote beating, enhance the rate of contractile protein synthesis and inmate myofibtillar reorganization in primary cultures of adult feline cardiac myocytes. Since occupaaon of the p receptor elevates [Ca2+]i, a question remains, do changes in Ca2+ flux regulate protein synthesis? Cultured feline myocytes were exposed to isoproterenol (ISO) in the presence or absence of KCl, nifedipine (N) or ryanodine (R) and the synthesis of total protein (TP), actin (A) and myosin heavy chain (MIX) was monitored by a sensitive pulse/equilibrium approach. IS0 (IOpM) elevated TP (18%), A (31%) and MIX (42%) when compared to values derived from quiescent controls. Depolarizing the sarcolemma with KC1 (5OmM) partially blunted the rise in TP, A and MHC synthesis, whereas exposing myocytes to IS0 plus N (1OpM) significantly depressed the synthesis of TP, A and MIX. IS0 and N also provoked a marked disruption in myotibrii structure. R (2OpM) inhibited IS?induced contractile protein synthesis but did not depress them below control values; moreover, R did not initiate myofibrillar breakdown. N or R completely blocked ISO-induced contractile activity, while myocytes “twitched” occasionally in the presence of KCl. The present observations suggest that blocking the entry of Ca2+ through the sarcolemmal Ltype Ca2+ channel is crucial in modulating contractile protein synthesis and myofibrillar organization; furthermore, contractile activity and not ISO, itself, appears to accelerate contractile protein synthesis in these cultured adult heart cells. 5.28