Renal potassium adaptation: role of the Na+-K+ pump in rat cortical collecting tubules

To evaluate the mechanism of renal potassium adaptation we explored several facets of Na+-K+-ATPase function during K loading in rat cortical collecting tubule (CCT). Urinary K excretion increased within the 1st day after initiation of dietary loading to a level matching intake, indicating the early onset of K adaptation. CCT Na+-K+-ATPase activity after 1 and 2 days on the high-K diet was not different from that observed in control animals, whereas it increased to threefold base line after 7 days. Similarly, the specific binding of ouabain was unchanged by 2 days of high-K diet, but was increased on the 7th day. In contrast, there was an early increase in Rb uptake that persisted throughout the period of observation. Acute (60 min) KCl infusion into control rats led to a significant increase in Rb uptake, whereas Na+-K+-ATPase hydrolytic activity remained unchanged. In the isolated perfused kidney, increasing perfusate K led to an increase in CCT Rb uptake similar to that observed in vivo, again without altering the hydrolytic activity of the enzyme. We conclude that K adaptation is an early event developing rapidly after initiation of dietary change. In its early phase the Na+-K+ pump responds by increasing K-transport rate to accommodate the acute homeostatic need; when the requirement for increased K secretion is sustained, a different adaptive pattern emerges characterized by an increase in the number of pumps. The adaptive response to an acute K load appears to be an intrinsic property of the pump independent of hormonal influences.