Temperature dependence of cardiac sarcoplasmic reticulum and sarcolemma in the ventricle of catfish (Clarias gariepinus)

The present study was undertaken to examine the relative contribution of the SR-Ca²⁺ release and sarcolemmal Ca²⁺ channels in developing the cardiac force at two different temperatures (20 and 30 °C) in the catfish (Clarias gariepinus).

The sarcolemmal Ca²⁺ contribution of activator Ca²⁺ was greater at a test temperature of 30 °C as assessed by verapamil. Whereas the SR-Ca²⁺ contribution was higher at 20 and 30 °C and a frequency rate of 0.2 and 0.4 Hz as assessed by caffeine and adrenaline, respectively. Bradykinin potentiating factor (BPF₇) which was isolated from jelly fish (Cassiopea andromeda) decreased the cardiac force developed at a frequency rate of 0.2 Hz and a temperature of 20 °C, whereas it increased the force developed at frequency rates of 0.2 and 0.4 Hz at 30 °C. These results indicate that BPF₇ may act like verapamil in reducing the cardiac force through blocking the sarcolemmal Ca²⁺ channels at low temperature and like adrenaline in an increase of the cardiac force developed at warm temperature and the high frequency rate through stimulation of SR-Ca²⁺ activator. Therefore, this study indicates that the sarcolemmal Ca²⁺ influx and the SR-Ca²⁺ release contributors of activator Ca²⁺ for cardiac force development in the catfish heart were significantly greater at warm temperature and at the pacing frequency rates of 0.2 and 0.4 Hz as assessed by verapamil, adrenaline, caffeine and BPF₇. However, the relative contribution of the sarcolemmal Ca²⁺ influx in the development of cardiac force in the catfish heart was greater than that of SR-Ca²⁺ release.