Intracellular pH in OK cells. II. Effects of temperature on cell pH.

Intracellular pH (pHi) is known to acidify as temperature rises. It has been proposed that this relationship reflects the temperature dependence of the dissociation constant of intracellular buffers. The purpose of this study was to evaluate whether H+ production and membrane acid/base transport events also contribute to the temperature dependence of pHi. This relationship was studied by means of the 490/450-nm fluorescence of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, to measure pHi of OK cells grown on cover slips and perfused in a thermostated chamber. As temperature was increased from 12 degrees C, pHi progressively acidified, until a precipitous and large alkalinization appeared at 40-45 degrees C. We specifically examined the range from 25 to 37 degrees C, over which pHi acidified by 0.32 units from 7.50 to 7.18. The three major components that regulate pHi in the OK cell were quantitated as follows: H+ production, H+ extrusion via Na(+)-H+ antiport, and the passive H+ leak from buffer to cell. Relative to the rate at 25 degrees C, acid production at 37 degrees C increased by 129% (3.82 +/- 0.78 vs. 8.76 +/- 1.12 mmol.l-1.min-1). The recovery of pHi after NH4Cl loading was used to measure the rate of Na(+)-H+ antiport, and in Na(+)-free depolarized cells the magnitude of passive H+ conductance through the leak pathway. Compared with the rate at 25 degrees C, at 37 degrees C the Na(+)-H+ antiport increased by 26% (1.25 +/- 0.22 vs. 1.58 +/- 0.25 mmol.l-1.min-1) and the H+ permeability increased by 140% (0.005 +/- 0.001 vs. 0.012 +/- 0.003 cm/s).(ABSTRACT TRUNCATED AT 250 WORDS)