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

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.