Effects of extracellular calcium and potassium on the sodium pump of rat adrenal glomerulosa cells.
Because the activity of the sodium pump (Na-K-ATPase) influences the secretion of aldosterone, we determined how extracellular potassium (K(o)) and calcium affect sodium pump activity in rat adrenal glomerulosa cells. Sodium pump activity was measured as ouabain-sensitive (86)Rb uptake in freshly dispersed cells containing 20 mM sodium as measured with sodium-binding benzofluran isophthalate. Increasing K(o) from 4 to 10 mM in the presence of 1.8 mM extracellular calcium (Ca(o)) stimulated sodium pump activity up to 165% and increased intracellular free calcium as measured with fura 2. Increasing K(o) from 4 to 10 mM in the absence of Ca(o) stimulated the sodium pump approximately 30% and did not increase intracellular free calcium concentration ([Ca(2+)](i)). In some experiments, addition of 1.8 mM Ca(o) in the presence of 4 mM K(o) increased [Ca(2+)](i) above the levels observed in the absence of Ca(o) and stimulated the sodium pump up to 100%. Ca-dependent stimulation of the sodium pump by K(o) and Ca(o) was inhibited by isradipine (10 microM), a blocker of L- and T-type calcium channels, by compound 48/80 (40 microg/ml) and calmidizolium (10 microM), which inhibits calmodulin (CaM), and by KN-62 (10 microM), which blocks some forms of Ca/CaM kinase II (CaMKII). Staurosporine (1 microM), which effectively blocks most forms of protein kinase C, had no effect. In the presence of A-23187, a calcium ionophore, the addition of 0.1 mM Ca(o) increased [Ca(2+)](i) to the level observed in the presence of 10 mM K(o) and 1.8 mM Ca(o) and stimulated the sodium pump 100%. Ca-dependent stimulation by A-23187 and 0.1 mM Ca(o) was not reduced by isradipine but was blocked by KN-62. Thus, under the conditions that K(o) stimulates aldosterone secretion, it stimulates the sodium pump by two mechanisms: direct binding to the pump and by increasing calcium influx, which is dependent on Ca(o). The resulting increase in [Ca(2+)](i) may stimulate the sodium pump by activating CaM and/or CaMKII.
Yingst
D R
DR
Department of Physiology, Wayne State University School of Medicine and the John D. Dingell Veterans Medical Center, Detroit, Michigan 48201, USA. dyingst@med.wayne.edu
Davis
J
J
Schiebinger
R
R
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000450:Aldosterone / Q000378:metabolism*; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D002147:Calmodulin / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D007093:Imidazoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D017275:Isradipine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012414:Rubidium Radioisotopes; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects* / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D015384:Zona Glomerulosa / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure
D015220:Calcium Channels; D002147:Calmodulin; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007476:Ionophores; D012414:Rubidium Radioisotopes; D000001:Calcimycin; D000450:Aldosterone; C031938:calmidazolium; C063302:KN 62; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase; D019311:Staurosporine; D011188:Potassium; D002118:Calcium; D017275:Isradipine