Effects of extracellular calcium and potassium on the sodium pump of rat adrenal glomerulosa cells

• Published in: American Journal of Physiology: Cell Physiology 2001-01, Vol.280 (1), p.C119-C125
• Main Authors: Yingst, Douglas R, Davis, Joanne, Schiebinger, Rick
• Format: Article
• Language: English
• Subjects: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine - analogs & derivatives; 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine - pharmacology; Aldosterone - metabolism; Aldosterone - secretion; Animals; Calcimycin - pharmacology; Calcium - metabolism; Calcium - pharmacology; Calcium Channels - drug effects; Calcium Channels - metabolism; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Calcium-Calmodulin-Dependent Protein Kinases - drug effects; Calcium-Calmodulin-Dependent Protein Kinases - metabolism; Calmodulin - drug effects; Calmodulin - metabolism; Cells, Cultured; Enzyme Inhibitors - pharmacology; Extracellular Space - drug effects; Extracellular Space - metabolism; Female; Imidazoles - pharmacology; Intracellular Fluid - drug effects; Intracellular Fluid - metabolism; Ionophores - pharmacology; Isradipine - pharmacology; Potassium - metabolism; Potassium - pharmacology; Rats; Rats, Sprague-Dawley; Rubidium Radioisotopes; Sodium-Potassium-Exchanging ATPase - drug effects; Sodium-Potassium-Exchanging ATPase - metabolism; Staurosporine - pharmacology; Zona Glomerulosa - drug effects; Zona Glomerulosa - metabolism; Zona Glomerulosa - ultrastructure
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.2001.280.1.c119

Departments of 1  Physiology and 2  Internal Medicine, Wayne State University School of Medicine and the John D. Dingell Veterans Medical Center, Detroit, Michigan 48201 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 ~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 µM), a blocker of L- and T-type calcium channels, by compound 48/80 (40 µg/ml) and calmidizolium (10 µM), which inhibits calmodulin (CaM), and by KN-62 (10 µM), which blocks some forms of Ca/CaM kinase II (CaMKII). Staurosporine (1 µM), 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. ouabain; signaling; Na-K-ATPase; calmodulin; calcium- and calmodulin-dependent kinase II; aldosterone