Tumor-promoting phorbol esters inhibit cardiac functions and induce redistribution of protein kinase C in perfused beating rat heart.

Abstract

Activation of protein kinase C has been implicated in the regulation of a variety of cellular reactions. Although we, and others, have found protein kinase C and its substrate proteins to be present in both membrane and cytosolic fractions in the heart, the physiologic role of this kinase in the regulation of cardiac functions remains unknown. In the present study, we found that in isolated perfused rat heart, administration of phorbol esters 4/3-phorbol 12,13-dibutyrate(PDBu) and 12-0-tetradecanoylphorbol 13-acetate(TPA), which are specific activators of protein kinase C, produced marked dose-dependent negative changes in inotropy and chronotropy. A dose-dependent decrease in coronary flow was also observed. The diacylglycerol analogues, 1,2-oleoylacetyl-glycerol and 1,2-dioctanoylglycerol, produced similar effects as the active phorbol esters on these isolated perfused hearts. An inactive analogue of phorbol ester, 4a-phorbol, failed to produce any effect. Protein kinase C activity in both membrane and cytosolic fractions prepared from rat heart could be activated by TPA and PDBu at the same concentration range as used in the experiments with perfused hearts. Following perfusion of the hearts with PDBu, a rapid translocation of protein kinase C from cytosolic to membrane fractions was also observed. Our findings provide the first direct evidence that protein kinase C may play a potentially important role in the regulation of cardiac functions. (Circulation Research 1987;61:372-378) C ardiac functions are regulated by various hormones, neurotransmitters, and drugs, which are thought to interact with specific receptors located on the sarcolemmal membrane.1 Activation of /3-adrenergic receptor elevates cyclic adenosine 3',5' monophosphate (cAMP) in the myocardium and induces positive inotropic and chronotropic responses. Cyclic AMP-dependent protein kinase in the heart phosphorylates Ca 2+ channels, thereby increasing Ca 2+ concentration inside the cell. 2 However, the cellsurface-transducing system of Ca 2+ -mobilizing receptors in the heart, and the second messenger system that mediates the inhibitory response of cardiac tissue, have yet to be elucidated.Nishizuka and his colleagues 3 first demonstrated that diacylglycerol (DAG) activates protein kinase C. Since then, a link between phosphatidylinositol (PI) turnover and protein kinase C activation in a variety of cellular responses to hormonal stimulation has been established. Intracellular activation of protein kinase C can be achieved by the addition of cell-membrane- This work supported by grant Tl-51 from the Ontario Heart Foundation. S. Y. was the recipient of a studentship from Connaught Award Foundation, University of Toronto.Address for correspondence: Amar K. Sen, MD, PhD, Department of Pharmacology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada M5S 1A8.Received July 7, 1986; accepted April 10, 1987. permeable DAG analogues. Tumor-promoting phorbol esters such as 4/3-phorbol 12,13-dibutyrate (PDBu) and 12-0-tetradecanoylp...

Phosphorylation-dependent Regulation of Cardiac Na+/Ca2+ Exchanger via Protein Kinase C

“…8). These findings are consistent with many previous studies that demonstrated that phorbol ester and synthetic diacylglycerol, and also ␣-adrenergic agonists and angiotensin II under certain conditions, exert significant depressive effects on the contractile function in a variety of cardiac preparations (33)(34)(35)(36)(37) and reduce diastolic [Ca 2ϩ ] i as well as Ca 2ϩ transient peaks in isolated perfused heart (36) and isolated adult cardiomyocytes (35,37). Since phorbol ester and exogenous diacylglycerol do not enhance phosphorylation of phospholamban in the sarcoplasmic reticulum in intact cardiomyocytes (38,39), increased Ca 2ϩ extrusion across the sarcolemma is the most likely mechanism for the observed decrease in [Ca 2ϩ ] i .…”

Phorbol ester activation of chloride current in guinea‐pig ventricular myocytes

“…The latter were more pronounced at + 40 mV than at -80 mV, and were usually not reversed by 5-10 min washouts with control solution, a difficulty previously reported in regard to other cardiac effects of phorbol esters (e.g. Yuan et al, 1987;Tseng & Boyden, 1991). However, stimulations produced by shorter treatments with moderate concentrations of PMA were reversible on occasion (see Figure 5).…”

Pharmacological characteristics of the positive inotropic effect of angiotensin II in the rabbit ventricular myocardium

“…Inhibition by PDBu of the agonist-induced phosphoinositide hydrolysis and functional changes have been demonstrated in a variety of cells, including smooth muscle cells (Brock et al, 1985), platelets (Kagaya et al, 1990) and myocardial cells (Yuan et al, 1987). In addition, in chick embryo myocytes, PDBu decreased Ca2+ transients increased by All and PMA inhibited the Allmediated increase in Ca2l transients in rat myocytes (Kem et al, 1991).…”