Ionic regulation of intracellular pH in rat calvarial osteoblasts

1. Intracellular pH of cultured rat calvarial osteoblasts was monitored continuously using the pH-sensitive fluorescent probe bis-carboxyethyl carboxyfluorescein. 2. Recovery from an intracellular acid load brought about by exposure to ammonium chloride was dependent on external sodium and blocked by the sodium-hydrogen exchange inhibitor amiloride (1 mM), indicating the presence of a plasma membrane sodium-hydrogen exchanger. 3. A SITS- (4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid) sensitive alkalinization occurred on the isosmotic replacement of external chloride by gluconate, suggesting the presence of chloride-bicarbonate exchange. 4. The dependence of the rate of sodium-hydrogen exchange on external sodium followed first-order kinetics, but the rate of exchange appeared to be sensitive to intracellular pH. 5. The rate of alkalinization brought about by the isosmotic replacement of chloride was sensitive to external bicarbonate concentration, but independent of external sodium. 6. Sodium-hydrogen exchange appeared to be inhibited and chloride-bicarbonate exchange stimulated by 1-34 parathyroid hormone.