Human Trabeculae Research Articles

Effect of protein kinase C activation on sarcoplasmic reticulum function and apparent myofibrillar Ca2+ sensitivity in intact and skinned muscles from normal and diseased human myocardium.

Protein kinase C regulates the activity of a diverse group of cellular proteins including membrane ion channel proteins. Although protein kinase C and its substrate protein have been identified in both membrane and cytosolic fractions in the heart, the physiological role of this kinase in the regulation of cardiac function remains unknown. We examined the physiological role of protein kinase C by stimulating its activity with 12-deoxyphorbol 13 isobutyrate 20 acetate (DPBA) in human trabeculae carneae. This resulted in decreased peak isometric twitch force and peak intracellular sarcoplasmic reticulum calcium release as detected with aequorin. Furthermore, in the presence of DPBA, steady-state force-[Ca2+] relations were shifted to higher intracellular calcium concentrations, and the Hill coefficient was reduced, indicating a decrease in responsiveness of the myofilaments to calcium and a change in cooperativity among thin filament proteins, respectively. Thus, DPBA affects not only intracellular calcium concentration, but myofilament calcium interactions as well. The effect of DPBA on Ca2+ activation probably reflects phosphorylation of thin-filament regulatory proteins by protein kinase C.

Effects of MCI-154 on Ca 2+ activation of skinned human myocardium

We investigated the effects of MCI-154, a new inotropic agent, on tension development in saponin-skinned human trabeculae carneae. The skinned fibers were activated by buffer solutions containing varying concentrations of Ca 2+ (10 −8-10 −4 M). In the sigmoidal tension vs. pCa (−log[Ca 2+]M) relationship, the Ca 2+ concentration required for half-maximal activation was shifted leftward in the presence of MCI-154. Furthermore, maximal Ca 2+-activated tension development was increased in a concentration-dependent manner by MCI-154. Our results suggest that the inotropic effect of MCI-154 may be due, in part, to an increased sensitivity of the myofilaments to Ca 2+ and enhancement of maximal Ca 2+-activated tension development.