Effects of High-K Low-Na, Diltiazem, Caffeine and Ba on Spontaneous Fluctuating Contractile Activities in Rat Cardiac Muscle

Abstract

ISHIDE, N., WATANABE, H. and TAKISHIMA, T. Effects of High-K Low-Na, Diltiazem, Caffeine and Ba on Spontaneous Fluctuating Contractile Activities in Rat Cardiac Muscle. Tohoku J. exp. Med., 1984, 144 (4), 331-341 - The effects of 1) high-K low-Na, 2) caffeine, 3) diltiazem and 4) Ba on spontaneous fluctuating contractile activity were examined in isolated rat trabecular muscles. Intracellular contractile activity was recorded by means of light intensity fluctuation at a point on a magnified image of the muscle illuminated by laser light. Perfusion with a high-K (124mM) low-Na (25mM) solution increased the root mean square (RMS) values of the light intensity fluctuations. Perfusion with the normal solution after this perturbation decreased the RMS values below those in the initial control. Caffeine (above 2.5mM) markedly decreased the RMS values. Diltiazem (0.1mM or 1mM) did not change the RMS values. Ba (2.0mM) without Ca reduced the RMS values. These observations suggest that the spontaneous fluctuating contractile activity is due to oscillating movements of Ca between contractile machinery and sarcoplasmic reticulum, and that Na/Ca exchange modulates these movements but Ca current through the slow channel does not influence these movements during resting periods