Cardiac Purkinje fibres

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Abstract
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, gK∞, 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, Erev, which followed log [K+]0 with 60 mV for a tenfold change. Since Erev obtained during Ca injection agreed with Erev 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 ∞.

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