Activation of Na+/H+ exchange on rat preadipocyte plasma membrane and its role in cell proliferation and differentiation

An in vitro cultured rat perirenal preadipocyte (PA) was established as a m odel system to investigate the role of the intracellular pH (pHi) and of th e Na+/H+ exchanger during PA proliferation and differentiation. pH sensitiv e probe, 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein(BCECF), was emp loyed to measure the pHi of PA and to determine the Na+/H+ exchange activit y. The results showed that there was Na+/H+ exchange activity in the plasma membrane of PA, FCS stimulated DNA synthesis measured by H-3-TdR incorpora tion, and the activation of Na+/H+ exchanger resulted in pHi increase (near ly 0.2 PH unit) within 2 min. Ethyl-isopropyl-amiloride (EIPA), a specific Na+/H+ exchange inhibitor, inhibited Na+/H+ exchange activity and DNA synth esis. In the absence of serum insulin did not stimulate DNA synthesis but d id induce PA differentiation characterized by the appearance of adiposome i n the cell and the enhancement of glycerol-3-phosphate dehydrogenase (G(3)P DHase) activity. Meantime, insulin was also found to stimulate Na+/H+ excha nge activity and pHi increase. EIPA. inhibited Na+/H+ exchanger activation induced by insulin and also partially inhibited the enhancement of G(3)PDHa se activity. These results demonstrated that the activation of Na+/H+ excha nge and the resulting pHi increase are the early events related to both pro liferation and differentiation of PA.