title: Evidence for increased in vivo sodium-potassium pump activity and potassium efflux in skeletal muscle of spontaneously hypertensive rats.
abstract: We have used 87Rb nuclear magnetic resonance spectroscopy (NMR) to study in vivo rubidium kinetics in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls, using rubidium as a marker for potassium. We gave 15 male, 13-week-old SHR, mean +/- s.d. blood pressure 180 +/- 10 mmHg, and 15 age-matched normotensive controls, mean blood pressure 120 +/- 9 mmHg, a daily dose of RbCl (2 mmol/kg intraperitoneally). We made repeated NMR measurements of skeletal muscle rubidium concentrations until steady state was reached. We then withdrew rubidium and made further measurements of rubidium concentrations, at intervals, for up to 1 week after the last injection. We also measured plasma and erythrocyte rubidium concentrations by flame atomic absorption spectroscopy at similar intervals after the withdrawal of rubidium. Rubidium concentrations rose at a faster rate in SHR skeletal muscle, but the steady-state muscle rubidium concentration was the same (45 mmol/l) in both SHR and WKY rats. There was also a threefold increase in the rate of rubidium efflux from both muscle and erythrocytes in SHR. These results are consistent with a marked increase in Na+,K(+)-ATPase activity and an increase in the rate of rubidium efflux in vivo in SHR. The increased rate of rubidium efflux in SHR could represent increased K+ efflux via calcium-activated K+ channels and/or result as part of cell volume regulation secondary to increased Na(+)-H+ antiporter activity.
authors.affiliation: MRC Unit, Radcliffe Infirmary, Oxford, UK.
authors.forename: P D
authors.initials: PD
authors.lastname: Syme
authors.forename: R M
authors.initials: RM
authors.lastname: Dixon
authors.forename: J K
authors.initials: JK
authors.lastname: Aronson
authors.forename: D G
authors.initials: DG
authors.lastname: Grahame-Smith
authors.forename: G K
authors.initials: GK
authors.lastname: Radda
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009132:Muscles / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D015221:Potassium Channels; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium