Apical membrane potassium channels in frog diluting segment: stimulation by furosemide.
The patch-clamp technique was used to study the activity of apical membrane potassium channels in frog isolated everted diluting segments, and the effect of transport inhibitors on channel activity was assessed. In cell-attached patches with a high-potassium pipette solution and Ringer in the bath the channels show inward rectification (inward conductance, 25.1 pS; outward conductance, 10.5 pS). The channel is selective for potassium over sodium and is voltage dependent with depolarization increasing channel open probability (Po). Furosemide increased channel activity, which resulted exclusively from a significant increase in the number (N) of channels in the patch (control, 2.3 +/- 0.3, n = 8; furosemide, 4.0 +/- 0.4, n = 14) without any significant change in Po. Amiloride blocked the stimulatory effect of furosemide by reducing N to 1.4 +/- 0.6 (n = 6), and amiloride alone also reduced N with no significant change in Po. This suggests that the increase in N in response to furosemide may be secondary to a rise in intracellular pH mediated by activation of the apical Na-H exchanger.
Hurst
A M
AM
Department of Physiology, Leeds University, United Kingdom.
Hunter
M
M
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D004553:Electric Conductivity; D004594:Electrophysiology; D005665:Furosemide / Q000494:pharmacology*; D007684:Kidney Tubules / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D011896:Rana temporaria; D013327:Strophanthidin / Q000494:pharmacology
D015221:Potassium Channels; D013327:Strophanthidin; D000584:Amiloride; D005665:Furosemide; D002118:Calcium