, Volume 316, Issue 1, pp 1-25

Two modes of Na extrusion in cells from guinea pig kidney cortex slices

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Summary

Cells from guinea pig kidney cortex slices, which have been loaded with Na and caused to lose K, by leaching at 0.6° C for 2.5 hours, extrude Na with Cl upon rewarming to 25° C in a medium without K. A subsequent rise in the K concentration in the bath at 25° C induces further net Na extrusion, 1 Na being extruded in exchange for 1 K that is taken up. When the leached tissue is rewarmed to 25°C in the presence of K in the bathing fluid (2 or 16 mM), some Na is extruded accompanied with Cl (by a mechanism that is inhibited by ethacrynic acid) and some Na is extruded maintanining a 1:1 ratio with the K that is taken up, (this system being inhibited by ouabain). Thus two modes of Na extrusion are observed, mode A that is accompanied by net Cl efflux, and that is inhibited by 2 mM ethacrynic acid, but not by 1 or 10 mM ouabain and mode B in which one K is taken up for each Na extruded. Mode B is inhibited by 1 mM ouabain and not by ethacrynic acid. DNP and anoxia inhibit both modes A and B. Insufficient doses of ouabain do not explain the refractoriness of mode A to ouabain. Ouabain and ethacrynic acid are known inhibitors of the Na−K-ATPase at much lower doses. It is concluded that both modes may originate in different Na pumps which may have different energy sources. Pump A should be efficient in the volume regulation of the cell. According to experimental procedure, both modes of Na extrusion appear of comparable magnitude. In the steady-state their relative role may be different.