The effect of thermal stress on electrical and mechanical responses and associated calcium movements of flounder heart and gut

1. 1. Contractile amplitude in the flounder auricle, ventricle and gut fell in response to temperature increase above the normal ambient temperature of 10°C. 2. 2. In whole heart and gut, the preparations were seen to hyperpolarize as temperature increased above 10°C, followed by a secondary depolarization. 3. 3. The amplitude of the cardiac action potential was not affected by temperature increase but the duration of the plateau phase was reduced. The amplitude of ileal muscle slow waves was reduced as temperature increased and above 30°C slow wave generation ceased. 4. 4. Radiocalcium flux studies showed that calcium influx into isolated ventricular and ileal strips fell as temperature was raised above ambient. 5. 5. Radiocalcium efflux from isolated ventricular and ileal muscle microsomes declined as temperature was raised above ambient. 6. 6. The negative inotropism and chronotropism seen with increasing temperature suggests a dysfunction in oscillatory slow wave cycles possibly related to denaturation of the electrogenic Na +/K + ATPase pump.