MECHANISM OF APICAL K- EFFECT OF INHIBITION OF BASOLATERAL NA+-K+-ATPASE( CHANNEL MODULATION IN PRINCIPAL RENAL TUBULE CELLS )

The effects of inhibition of the basolateral Na+-K+-ATPase (pump) on t he apical low-conductance K+ channel of principal cells in rat cortica l collecting duct (CCD) were studied with patch-clamp techniques. Inhi bition of pump activity by removal of K+ from the bath solution or add ition of strophanthidin reversibly reduced K+ channel activity in cell -attached patches to 36% of the control value. The effect of pump inhi bition on K+ channel activity was dependent on the presence of extrace llular Ca2+, since removal of Ca2+ in the bath solution abolished the inhibitory effect of 0 mM K+ bath. The intracellular [Ca2+] (measured with fura-2) was significantly increased, from 125 nM (control) to 335 nM (0 mM K+ bath) or 408 nM (0.2 mM strophanthidin), during inhibitio n of pump activity. In contrast, cell pH decreased only moderately, fr om 7.45 to 7.35. Raising intracellular Ca2+ by addition of 2 muM ionom ycin mimicked the effect of pump inhibition on K+ channel activity. 0. 1 mM amiloride also significantly reduced the inhibitory effect of the K+ removal. Because the apical low-conductance K channel in inside-ou t patches is not sensitive to Ca2+ (Wang, W., A. Schwab, and G. Giebis ch. 1990. American Journal of Physiology. 259:F494-F502), it is sugges ted that the inhibitory effect of Ca2+ is mediated by a Ca2+-dependent signal transduction pathway. This view was supported in experiments i n which application of 200 nM staurosporine, a potent inhibitor of Ca2 +-dependent protein kinase C (PKC), markedly diminished the effect of the pump inhibition on channel activity. We conclude that a Ca2+-depen dent protein kinase such as PKC plays a key role in the downregulation of apical low-conductance K+ channel activity during inhibition of th e basolateral Na+-K+-ATPase.