Turnover rate of the cardiac Na(+)‐Ca2+ exchanger in guinea‐pig ventricular myocytes.

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