pH regulation of K (+) efflux from myocytes in isolated rat hearts: (87) Rb, (7) Li, and (31) P NMR studies
Kupriyanov, V.V.; Xiang, B.; Kuzio, B.; Deslauriers, R.
American Journal of Physiology 277(1): H279-H289
1999
ISSN/ISBN: 0002-9513 PMID: 10409207 Document Number: 506890
This study investigates the effects of intracellular (pHi) and extracellular pH (pHe) on the efflux of Rb+ and Li+ in isolated rat hearts. 87Rb and 7Li NMR were used to measure Rb+ and Li+ content, respectively, of hearts, and 31P NMR was used to monitor pHi, pHe, and phosphate levels. After 30-min equilibration with Rb+ or Li+, effluxes were initiated by switching perfusion to a Rb+- or Li+-free, high-K+ (20.7 mM) Krebs-Henseleit buffer with 15 mM bumetanide. Monensin (2 mM) increased pHi from 7.10 ± 0.05 to 7.32 ± 0.07 and resulted in activation of Rb+ efflux; the first-order rate constant (k 103, in min-1) increased from 42 ± 2 to 116 ± 16. Glibenclamide (4 mM) did not inhibit monensin-activated Rb+ efflux (k = 110 ± 17), whereas quinine (0.2 mM) slightly inhibited it by 19 ± 9%. Infusion of 15 mM NH4Cl during Rb+ washout increased k for Rb+ efflux by 93% (81 ± 8), which was glibenclamide and quinine insensitive, and caused a transient increase in pHi to 7.25 ± 0.08. Intracellular Li+ inhibited NH4Cl-stimulated Rb+ efflux by 55%. Monensin and NH4Cl stimulated Li+ efflux by 40%, increasing k from 29 ± 3 to 43 ± 7 and 41 ± 3, respectively. The stimulation was not sensitive to 10 mM dimethylamiloride. Intracellular acidosis that resulted from the washout of NH4Cl (pH 6.86 ± 0.2) slightly inhibited Rb+ efflux (k = 36 ± 5), whereas NH4Cl itself in the absence of pHi changes did not markedly affect Rb+ efflux. A moderate increase in pHi (7.17 ± 0.06) produced by washout of 15 mM 2,2-dimethylpropionate (DMP)-Tris from hearts preequilibrated with DMP did not markedly affect Rb+ efflux. Neither global alkalosis (pHi 7.4, pHe 7.55) nor acidosis (pHi ~ pHe 6.8) produced by 3 mM Tris base or 5 mM MES, respectively, affected Rb+ efflux. We suggest that intracellular alkalosis stimulates Rb+ (K+) and Li+ effluxes by activating a nonselective sarcolemmal K+ (Li+)/cation exchanger or a K+ (Li+)-anion symporter. Reprinted by permission of the publisher.