Activation of furosemide-sensitive K+ fluxes in myocytes by ouabain and recovery from metabolic inhibition.
Modulation of transsarcolemmal K+ flux mediated by the furosemide-sensitive K(+)-Cl- (or Na(+)-K(+)-Cl-) cotransport carrier was studied in cultured chick embryo ventricular cells. We defined at least three distinct K+ efflux pathways: 1) a Ba2(+)-sensitive efflux component, probably reflecting K+ movement through K+ channels; 2) a furosemide-sensitive component, reflecting K(+)-Cl- cotransport; and 3) a component insensitive to both Ba2+ and furosemide. With respect to K+ influx, there were 1) a ouabain-sensitive K+ uptake presumably mediated by Na(+)-K(+)-adenosinetriphosphatase and 2) a furosemide-sensitive K+ uptake. The effects of elevation of intracellular calcium concentration ([Ca2+]i) on Ba2+ and furosemide-sensitive K+ flux pathways were studied. Elevation of [Ca2+]i had minor effects on Ba2(+)-sensitive K+ flux. However, elevation of [Ca2+]i produced by exposure to ouabain for 60 min activated a furosemide-sensitive 42K+ efflux and a ouabain-resistant, furosemide-sensitive 42K+ influx. The activation of K+ influx, caused by an increase in [Ca2+]i, was completely inhibited by ATP depletion (produced by exposure to ouabain and metabolic inhibitors simultaneously) and was partially inhibited by the calmodulin inhibitor W7. Activation of the furosemide-sensitive K+ flux was also produced by washout of metabolic inhibitors, a condition in which ATP resynthesis occurs in the presence of an increased [Ca2+]i. Activation of furosemide-sensitive K+ fluxes by exposure to ouabain or washout of metabolic inhibitors caused a net K+ loss, which accounts in part for the cell shrinkage noted during recovery from metabolic inhibition in previous studies. These results suggest that [Ca2+]i and intracellular ATP concentration are important in the regulation of furosemide-sensitive K+ flux in these cells, perhaps via the involvement of a Ca2(+)-calmodulin-dependent protein kinase.
Kohmoto
O
O
Department of Medicine, University of Utah School of Medicine, Salt Lake City 84132.
Krueger
J A
JA
Barry
W H
WH
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology*; D007038:Hypotonic Solutions / Q000494:pharmacology; D007477:Ions; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D027981:Symporters; D000096922:K Cl- Cotransporters
D000255:Adenosine Triphosphate; D002118:Calcium; D002352:Carrier Proteins; D002712:Chlorides; D005665:Furosemide; D007038:Hypotonic Solutions; D007477:Ions; D010042:Ouabain; D011188:Potassium; D011493:Protein Kinase C; D012964:Sodium; D027981:Symporters; D000096922:K Cl- Cotransporters