Protein tyrosine kinase regulates the number of renal secretory K channels

The apical small conductance (SK) channel plays a key role in K secretion i n the cortical collecting duct (CCD). A high-K intake stimulates renal K se cretion and involves a significant increase in the number of SK channels in the apical membrane of the CCD. We used the patch-clamp technique to exami ne the role of protein tyrosine kinase (PTK) in regulating the activity of SK channels in the CCD. The application of 100 mu M genistein stimulated SK channels in 11 of 12 patches in CCDs from rats on a K-deficient diet, and the mean increase in NP0, a product of channel number (N) end open probabil ity (P-0), was 2.5. In contrast, inhibition of PTK had no effect in tubules from animals on a high-K diet in all 10 experiments. Western blot analysis further shows that the level of cSrc, a nonreceptor type of PTK is 261% hi gher in the kidneys from rats on a K-deficient diet than those on a high-K diet. However, the effect of cSrc was not the result of direct inhibition o f channel itself, because addition elf exogenous cSrc had no effect on SK c hannels in inside-out patches. In cell-attached patches, application of her bimycin A increased channel activity in 14 of 16 patches, and the mean incr ease in NP0 was 2.4 in tubules from rats on a K-deficient diet. In contrast , herbimycin A had no effect on channel activity in any of 15 tubules from rats on a high-K diet. Furthermore, herbimycin A pretreatment increased NP0 per patch from the control value (0.4) to 2.25 in CCDs from rats on a K-de ficient diet, whereas herbimycin failed to increase channel activity (NP0: control, 3.10; herbimycin A, 3.25) in the CCDs from animals on a high-K die t. We conclude that PTK is involved in regulating the number of apical SK c hannels in the kidney.