Troglitazone induces a cellular acidosis by inhibiting acid extrusion in cultured rat mesangial cells

Abstract

We studied the effect of troglitazone on cellular acid-base balance and alanine formation in isolated rat mesangial cells. Mesangial cells were grown to confluency in RPMI 1640 media on 30-mm chambers used to monitor both cellular pH using the pH-sensitive dye 2'7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein and metabolic acid production as well as glutamine metabolism. Troglitazone (10 microM) induced a spontaneous cellular acidosis (6.95 +/- 0.02 vs. 7.47 +/- 0.04, respectively; P < 0.0001) but without an increase in lactic acid production. Alanine production was reduced 64% (P < 0.01) consistent with inhibition of the glutamate transamination. These findings pointed to a decrease in acid extrusion rather than an increase in acid production as the underlying mechanism leading to the cellular acidosis. To test their acid extrusion capabilities, mesangial cells were acid loaded with NH and then allowed to recover in Krebs-Henseleit media or in Krebs-Henseleit media minus bicarbonate (HEPES substituted), and the recovery response (Delta pH(i)/min) was monitored. In the presence of 10 microM troglitazone, the recovery response to the NH acid load was virtually eliminated in the bicarbonate-buffered media (0.00 +/- 0.001 vs. 0.06 +/- 0.02 pH(i)/min, P < 0.0001 vs. control) and reduced 75% in HEPES-buffered media (0.01 +/- 0.01 vs. 0.04 +/- 0.02 pH(i)/min, P < 0.002 vs. control). These results show that troglitazone induces a spontaneous cellular acidosis resulting from a reduction in cellular acid extrusion.