Temperature effects on the Na and Ca currents in rat and hedgehog ventricular muscle

Abstract

Cardiac transmembrane potentials and Na and Ca currents were recorded at different temperatures in rat and hedgehog ventricular muscle. At 35 °C in both species resting potential was about −80 mV and upstroke velocity ( V ̇ max ) of the action potential above 100 V s . The shape of the action p in hedgehog ventricular cells at 35 °C was similar to that in the rat showing a fast repolarization phase. When temperature was decreased, the membrane resting potential depolarized and action potential amplitude and V ̇ max declined. In rat ventricular cells at 10 °C, the resting potential was about −40 to −50 mV and V ̇ max was reduced to about 5 V s . In hedgehog ventricular cells, however, the tra potentials and V ̇ max were better maintained at low temperature. Phase 3 of the action potential was markedly prolonged below 20 °C in hedgehog but not in rat ventricular cells. When temperature was decreased to 10 °C the availability curve of the Na current shifted toward more negative potentials and I Ca,peak declined in rat ventricular cells. In hedgehog cardiac preparations, the Na current was less influenced by the cooling and I Ca,peak did not change very much at low temperatures. A transient inward current usually considered to induce cardiac arrhythmias could be recorded in rat ventricular cells below 20 °C but not in hedgehog preparations. These features of hedgehog cardiac membranes may contribute to the cold tolerance and the resistance to ventricular fibrillation during the hypothermia in mammalian hibernators.