Effect of ionomycin on cell pH in isolated renal proximal tubules

In isolated rabbit proximal tubules the addition of 2.0 microM but not 0.2 microM ionomycin induced a sustained increase in cell pH ([pH]i). This [pH]i response to 2.0 microM ionomycin was shown to be independent of several transporters such as Na+/H+ exchanger, Na(+)-HCO3- cotransporter, Cl-/HCO3- exchanger, or H(+)-ATPase. On the other hand, the removal of extracellular Ca2+ abolished the [pH]i increase or even induced a transient [pH]i decrease in the presence of ionomycin. These results are consistent with the induction of Ca2+/H+ exchange by ionomycin. Therefore Ca2+ ionophores should be used with caution as probes to estimate renal tubule functions.