Stimulation of protein kinase C rapidly reduces intracellular Na+ concentration via activation of the Na

Na1 reabsorption is regulated in proximal tubules by hormones that stimulate protein kinase C (PKC). To determine whether stimulation of PKC causes a reduction in intracellular Na1 concentration ([Na1]i) that might link Na 1 pump activation to increased Na1 reabsorption, [Na1]i was measured in kidney cells loaded with the Na1-sensitive fluorescent indicator SBFI. Rapid digital imaging fluorescence microscopy determinations were performed in epithelial kidney cells transfected with the rodent Na1 pump a1 cDNA. In 42 determinations, the basal [Na1]i was 19.7 6 2.4 mM. Stimulation of PKC reduced the [Na1]i to 5.6 6 0.6 mM in;10 sec. This drastic change in [Na 1]i requires a transient 74–120-fold increase in Na1 pump activity. After the new steady state [Na1]i is reached, the N