K+ channels in the basolateral membrane of rat cortical collecting duct are regulated by a cGMP-dependent protein kinase.
The basolateral membrane of the rat cortical collecting duct (CCD) principal cell is K+ conductive. Recently, two different K+ channels have been described, namely a small- and an intermediate-conductance K+ channel (s-K+ and i-K+) which most likely are responsible for the macroscopic K+ conductance. K+ channel activity was investigated at the single-channel level using the patch-clamp technique. Patch-clamp recordings were obtained from enzymatically isolated CCD segments and freshly isolated CCD cells using conventional cell-free, cell-attached, cell-attached-nystatin and slow-whole-cell methods. Both K+ channels showed rundown behaviour after excision. In an excised inside-out oriented membrane, K+ channels could be activated by simultaneous addition of 0.1 mmol/l (cyclic guanosine monophosphate (cGMP) and 0.1 mmol/l MgATP to the bath. The i-K+ was activated in 13 out of 45, the s-K+ in 15 out of 45, cases. No activation of either channel was observed with cGMP alone (0.1 mmol/l), MgATP alone (0.1 mmol/l), cGMP and guanosine triphosphate (GTP) (0.1 mmol/l each) or cyclic adenosine monophosphate (cAMP) and MgATP (0.1 mmol/l each) n = 15, 11, 7, 8, respectively). The activated s-K+ could be blocked by KT 5823 (n = 8), a specific inhibitor of a cGMP-dependent protein kinase (PKG). An inhibition of the activated i-K+ was seen in seven cases. The membrane potential hyperpolarized significantly after application of dibutyryl-cGMP (0.1 mmol/l, n = 6) or nitroprusside (10 mumol/l, n = 5), which is known to liberate NO and thus increase the intracellular cGMP level.(ABSTRACT TRUNCATED AT 250 WORDS)
Hirsch
J
J
Westfälische Wilhelms-Universität Münster, Medizinische Poliklinik, Experimentelle Nephrologie, Germany.
Schlatter
E
E
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001711:Biotransformation / Q000187:drug effects; D002227:Carbazoles; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007211:Indoles; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008387:Marine Toxins; D008566:Membranes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D009761:Nystatin / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000470:Alkaloids; D002227:Carbazoles; D007211:Indoles; D008387:Marine Toxins; D010080:Oxazoles; D015221:Potassium Channels; C073601:KT 5823; D009761:Nystatin; D009599:Nitroprusside; D003995:Dibutyryl Cyclic GMP; C059041:calyculin A; D000255:Adenosine Triphosphate; D017869:Cyclic GMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases