Tracing the Na/K-ATPase with rubidium.

Rubidium (Rb) was used as a marker ion for K to assess Na/K(Rb)-ATPase activity in single renal tubule cells. Initial Rb uptake rates were measured by electron microprobe analysis in individual tubule cells of the rat kidney during acute stimulation or during inhibition of transepithelial Na absorption. Under these conditions, Rb uptake closely correlates with intracellular Na concentrations, indicating that the intracellular Na concentration is a major determinant in the precise adjustment of basolateral, Na/K(Rb)-ATPase-dependent Na extrusion to Na entry across the apical cell membrane. Chronically increased distal Na delivery induced by loop diuretics triggers adaptive processes which allow increased transcellular Na movement at normal or near-normal intracellular Na concentrations.