Ca2+ mediates the effect of inhibition of Na+-K+-ATPase on the basolateral K+ channels in the rat CCD.
We investigated the effect of inhibiting Na+-K+-ATPase on the basolateral 18-pS K+ channel in the cortical collecting duct (CCD) of the rat kidney. Inhibiting Na+-K+-ATPase with strophanthidin decreased the activity of the 18-pS K+ channel and increased the intracellular Ca2+ to 420 nM. Removal of extracellular Ca2+ abolished the effect of strophanthidin. When intracellular Ca2+ was raised with 5 microM ionomycin or A-23187 to 300, 400, and 500 nM, the activity of the 18-pS K+ channel in cell-attached patches fell by 40, 85, and 96%, respectively. To explore the mechanism of Ca2+-induced inhibition, the effect of 400 nM Ca2+ on channel activity was studied in the presence of calphostin C, an inhibitor of protein kinase C, or KN-93 and KN-62, inhibitors of calmodulin-dependent kinase II. Addition of calphostin C or KN-93 or KN-62 failed to block the inhibitory effect of high concentrations of Ca2+ . This suggested that the inhibitory effect of high concentrations of Ca2+ was not mediated by protein kinase C or calmodulin-dependent kinase II pathways. To examine the possibility that the inhibitory effect of high concentrations of Ca2+ was mediated by the interaction of nitric oxide with superoxide, we investigated the effect of 400 nM Ca2+ on channel activity in the presence of 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron) or N(omega)-nitro-L-arginine methyl ester. Pretreatment of the tubules with 4,5-dihydroxy-1,3-benzenedisulfonic acid or N(omega)-nitro-L-arginine methyl ester completely abolished the inhibitory effect of 400 nM Ca2+ on channel activity. Moreover, application of 4,5-dihydroxy-1,3-benzenedisulfonic acid reversed the inhibitory effect of strophanthidin. We conclude that the effect of inhibiting Na+-K+-ATPase is mediated by intracellular Ca2+ and the inhibitory effect of high concentrations of Ca2+ is the result of interaction of nitric oxide with superoxide.
Department of Pharmacology, New York Medical College, Valhalla, NY 10595, USA.
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D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007685:Kidney Tubules, Collecting / Q000201:enzymology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009566:Nitrates / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D013047:Specific Pathogen-Free Organisms; D013327:Strophanthidin / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D000096926:Benzenesulfonamides
D001596:Benzylamines; D002118:Calcium; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D015759:Ionomycin; D007476:Ionophores; D019331:NG-Nitroarginine Methyl Ester; D009281:Naphthalenes; D009566:Nitrates; D015221:Potassium Channels; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase; D013327:Strophanthidin; D013449:Sulfonamides; D013481:Superoxides; C072105:KN 93; D000096926:Benzenesulfonamides; C039642:peroxynitric acid; C058819:calphostin C