Z. Su et al., INFLUENCE OF PRIOR NA+ PUMP ACTIVITY ON PUMP AND NA+ CA2+ EXCHANGE CURRENTS IN MOUSE VENTRICULAR MYOCYTES/, American journal of physiology. Heart and circulatory physiology, 44(5), 1998, pp. 1808-1817
We examined the dependence of peak Na+ pump and Na+/Ca2+ exchanger cur
rents on prior Na+ pump inhibition induced by exposure to zero extrace
llular K+ in voltage-clamped adult murine ventricular myocytes. Abrupt
activation of the Na+ pump by reexposure of myocytes to extracellular
K+ with a rapid solution switcher resulted in the development of a tr
ansient peak current at similar to 500 ms, followed by a decline over
1-2 min to a steady-state level. The magnitudes of both the peak Na+ p
ump current (I-p) and the peak outward Na+/Ca2+ exchange current, acti
vated by rapidly reducing extracellular Na+ to zero with the solution
switcher, were dependent on previous Na+ pump activity. [Na+] gradient
s (Na+-binding benzofuran isophthalate fluorescence) between the patch
pipette and the bulk cytosol were relatively small and could not acco
unt for the large differences between peak and steady-state I-p and re
verse Na+/Ca2+ exchanger currents. Our results are consistent with the
presence of a subsarcolemmal Na+ concentration gradient, which is sim
ilar for the Na+ pump and the Na+/Ca2+ exchanger. These findings also
support the hypothesis that the Na+ pump and the Na+/Ca2+ exchanger ar
e colocalized in the sarcolemma.