A stretch-activated K+ channel sensitive to cell volume.
The role of K+ channels in cell osmoregulation was investigated by using the patch-clamp technique. In cell-attached patches from Necturus proximal tubule, the short-open-time K+ channel at the basolateral membrane could be stretch-activated by pipette suction, where a negative pressure of 6 cm H2O (588.6 Pa) was sufficient to increase the open probability of the channel by a factor of 4.0 +/- 0.8 (n = 7 tubules). A 50% reduction in bath osmolarity increased cell volume by 66 +/- 10% and increased the K+-channel open probability by a factor of 5.8 +/- 1.4 (n = 7) in the same cell-attached patches that were activated by pipette suction. A kinetic analysis indicates one open state and at least two closed states for this epithelial K+ channel. Both suction and swelling shorten the longest time constant of the closed-time distribution by a factor of 3, without significant effect on either the mean open time or the shorter closed-state time constant. The similar effect of suction and swelling is consistent with the hypothesis that stretch-activated K+ channels mediate the increase in macroscopic K+ conductance that occurs during osmoregulation of amphibian proximal tubules. Calculations based on a simple model indicate that small increments in cell volume could produce statistically significant increases in K+-channel activity.
Sackin
H
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Department of Physiology and Biophysics, Cornell University Medical College, New York, NY 10021.
D000818:Animals; D001485:Basement Membrane / Q000502:physiology; D007038:Hypotonic Solutions; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D009337:Necturus; D015221:Potassium Channels / Q000502:physiology*; D012016:Reference Values; D014882:Water-Electrolyte Balance
D007038:Hypotonic Solutions; D015221:Potassium Channels