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Objective: Protein kinase C (PKC) is thought to be involved in the regulation of the mammalian cardiac excitation–contraction coupling process by vasoactive peptides like endothelin-1 (ET-1). However, the demonstration of a causal link between activation of specific PKC isoforms and the increase in contractility mediated by ET-1 is still inferential. Methods: By means of adenovirus-mediated gene transfer, we specifically overexpressed PKCϵ in cultured adult rabbit ventricular myocytes (Ad-PKCϵ). Myocyte shortening and [Ca2+]i transients under basal and ET-1-stimulated conditions were measured in Ad-PKCϵ and Ad-LacZ control transfected cells. Results: Infection with Ad-PKCϵ resulted in a strong, virus dose-dependent increase in PKCϵ protein levels, whereas protein expression of other PKC isoforms remained unchanged. Using a multiplicity of infection of 100 plaque-forming units/myocyte, basal and cofactor-dependent PKCϵ kinase activity was increased 28- and 90-fold, respectively, when compared to control. Myocyte basal fractional shortening and [Ca2+]i transient amplitude were both increased by 21% (P<0.05 each) in Ad-PKCϵ transfected myocytes when compared to Ad-LacZ transfected control myocytes. The positive inotropic effect of ET-1 in control myocytes was markedly blunted in PKCϵ-overexpressing myocytes. Conclusion: Specific overexpression of PKCϵ in rabbit ventricular myocytes increases basal myocyte contractility and [Ca2+]i transients, and modifies their responsiveness to ET-1. [ABSTRACT FROM PUBLISHER]

To study the cellular mechanisms of arrhythmias occurring in cardiac hypertrophy, we performed standard microelectrode studies on papillary muscles isolated from control (group N) and hypertrophied ferrets right ventricles. Different stages of hypertrophy, induced by pulmonary banding, were studied: 10-22 days (group H1), 4-6 weeks (H2), and 5 1/2-6 months (H3). During the development of hypertrophy, under β-adrenergic stimulation, triggered activity ITA) induced by delayed afterdepolarizations appeared in 2 of 5 muscles in group HI and 8 of 8 in group H2. This arrhythmia was absent in N muscles, as well as in H3, despite a pronounced prolongation of the action potentials at 50% (100 ± 9.3 msec in group H3 vs 67 ± 5.7 msec in H2; P < 0.01) and 90% of repalarization (225 ± 8.7 in H3 vs 185 ± 7.4 msec in H2: P < 0.02). The presence of TA was associated with an increase in the intracellular calcium activity (144 ± 60 nM in H2 vs 47 ± 9 nM in N; P < 0.05). TA properties were as follows. Triggering frequency increased as β-adrenergic stimulation increased, as pacing cycle length (PCL) decreased, and us duration of the prestimulative pause increased. The duration of salvos of TA increased as duration of the prestimulative pauses increased INS). The coupling interval of the first triggered beat decreased as PCL decreased (P < 0.1001). The minimal cycle length of salvos of TA was not modified by these parameters. It is concluded that delayed afterdepolarizations-induced TA may occur under β-adrenergic stimulation during the first stages of ventricular hypertrophy. This could partly explain the occurrence of adrenergic-dependent arrhythmias in ventricular hypertrophy. [ABSTRACT FROM AUTHOR]