K+ fluxes mediated by Na+‐K+‐Cl− cotransport and Na+‐K+‐ATPase pumps in renal tubule cell lines transformed by wild‐type and temperature‐sensitive strains of simian virus 40

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Abstract
The relative contributions of Na+‐+‐pumps and Na+‐+‐− contransport to total rubidium (Rb+) influx into primary cultures of renal tubule cells (PC.RC) and cells transformed either with the wild‐type or a temperature‐sensitive mutant of the simian virus 40 (SV40), were measured under various growth conditions. The Na+‐+‐mediated component represented 74% and 44–48% of total Rb+ influx into PC.RC and SV40‐transformed cells, respectively. Proliferating transformed cells showed substantial ouabain‐resistant bumetanide‐sensitive (Or‐Bs) Rb+ influx (41–45% of total) which indicated the presence of Na+‐+‐− contransport. The Or‐Bs component of Rb+ influx was greatly reduced when temperature‐sensitive transformed renal cells (RC.SVtsA58) grown in Petri dishes or on permeable filters were shifted from the permissive (33°C) to the restrictive temperature (39.5°C) to arrest cell growth. The ouabain‐sensitive Rb+ influx mediated by the Na+‐+‐, the total and amiloride‐sensitive Na+ uptakes were not modified following inhibition of cell proliferation. A similar fall in the Or‐Bs influx was obtained when renal tubule cells transformed by the wild‐type SV40 (RC.SV) were incubated with the K+ channel blocker, tetraethylammonium (TEA) ion, which we had previously shown to arrest cell growth without affecting cell viability (Teulon et al.: J. Cell. Physiol., 151:113–125, 1992). Reinitiation of cell growth by removal of TEA or return to 33°C of the temperature‐sensitive cells restored the Or‐Bs component of Rb influx. Taken together, these results indicate that the Na+‐+‐− cotransport activity is critically dependent on cell growth con ditions.

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