Cardiac Purkinje fibres

Summary

The influence of intracellular calcium concentration [Ca²⁺] _i on the steady state membrane currentsi _∞ was studied in a range of clamp potentials between −20 and −100 mV. Injection of CaCl₂ or Ca-EGTA (pCa ≤6) increasedi _∞ whereas injection of K-EGTA diminished it. The changes Δi _∞ were attributed to a change in steady state potassium conductance, g_K∞, by four arguments: Δi _∞ was restricted to potentials negative to −20 mV and depended on clamp potential in an inward rectifying manner. Δi _∞ displayed a reversal potential, E_rev, which followed log [K⁺]₀ with 60 mV for a tenfold change. Since E_rev obtained during Ca injection agreed with E_rev observed during EGTA injection the potassium driving force had to be constant. Wheng _K was blocked by superfusion with 20 mM Cesium neither CaCl₂ nor K-EGTA injection modifiedi _∞.