Stretch-activated potassium channels in renal proximal tubule.

A short open-time potassium (K) channel that has previously been identified in the basolateral membrane of Necturus proximal tubule (17) is activated by membrane stretch. Application of between 12 and 20 cmH2O negative pressure to the patch pipette reversibly increases mean number of open basolateral K channels (NP0) by a factor of 5.3 +/- 2 in cell-attached patches (n = 4) and a factor of 13.7 +/- 5 in excised patches (n = 8). This stretch activation does not alter channel selectivity or conductance and depends on neither the direction of K current nor the orientation of the patch ("inside-out" vs. "outside-out"). The increase in NP0 occurs within seconds after applying negative pressure to the patch and is proportional to applied negative pressure. Stretch activation of the basolateral potassium channel may play an important role in proximal tubule cell volume regulation. For example, if swelling stretches the basolateral membrane, the resulting increase in NP0 could restore cell volume by loss of K (with an accompanying anion) followed by osmotic exit of water.