TURNOVER RATE OF THE CARDIAC NA-CA2+ EXCHANGER IN GUINEA-PIG VENTRICULAR MYOCYTES()

1. Single guinea-pig ventricular myocytes were voltage clamped using t he whole-cell configuration of the patch-clamp technique and membrane current generated by the Na+-Ca2+ exchange mechanism recorded. 2. Rapi d increases in cytosolic free calcium ([Ca2+]i) evoked by flash photol ysis of either nitr-5 or DM-nitrophen resulted in current relaxations, arising from a redistribution of exchanger carrier conformations indu ced by the changes in [Ca2+]i. 3. Relaxation time constants were tempe rature dependent with a temperature coefficient over a 10-degrees-C ra nge (Q10) of approximately 3 and also voltage dependent, decreasing on hyperpolarization for membrane potentials in the range + 40 to - 80 m V. 4. The experimental results are consistent with consecutive exchang e models having electrogenic Na+ translocation steps, together with a site density and turnover rate similar to that for the Na+-K+ pump.