Na +/H + exchange is responsible for intracellular pH regulation in insulin-secreting HIT-T15 cells

Abstract

The addition of glucose to suspensions of HIT-T15 insulinoma cells caused a small, transient acidification followed by a gradual, progressive alkalinisation, as assessed by the fluorescent pH-sensitive dye 2',7'-biscarboxyethyl-5'-(6')-carboxyfluorescein (BCECF). Treatment of cells with acetate or lactate produced an immediate, marked acidification followed by recovery and a subsequent alkalinisation. In contrast, addition of NH 4C1 caused a rapid rise in intracellular pH (pHi) and recovery to resting values. In cells where Na +/H + exchange was inhibited, either with amiloride or by omission of Na + from the medium, glucose caused a progressive acidification, whilst recovery from acetate- or lactate-induced acidification was prevented. Under sodium-free conditions, recovery from acidification could be initiated by addition of Na +. Inhibition of HCO 3 −/C1 − exchange by pretreatment with 4,4'-diisothiocyanatostilbene 2,2'-disulphonic acid (DIDS), or by omission of HCO 3 − or Cl − from the medium did not affect any of the changes in pHi elicited by the above agents. It is concluded that the principal mechanism responsible for pHi regulation in HIT-T15 cells is the Na +/H + antiporter and that the HCO 3 −/C1 − exchange systems make little, if any, contribution.