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.