Abstract.
Amiloride-sensitive, Na+-dependent, DIDS-insensitive cytoplasmic alkalinization is observed after hypertonic challenge in Ehrlich ascites tumor cells. This was assessed using the fluorescent pH-sensitive probe 2′,7′-bis-(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF). A parallel increase in the amiloride-sensitive unidirectional Na+ influx is also observed. This indicates that hypertonic challenge activates a Na+/H+ exchanger. Activation occurs after several types of hypertonic challenge, is a graded function of the osmotic challenge, and is temperature-dependent. Observations on single cells reveal a considerable variation in the shrinkage-induced changes in cellular pH i , but the overall picture confirms the results from cell suspensions.
Shrinkage-induced alkalinization and recovery of cellular pH after an acid load, is strongly reduced in ATP-depleted cells. Furthermore, it is inhibited by chelerythrine and H-7, inhibitors of protein kinase C (PKC). In contrast, Calyculin A, an inhibitor of protein phosphatases PP1 and PP2A, stimulates shrinkage-induced alkalinization. Osmotic activation of the exchanger is unaffected by removal of calcium from the experimental medium, and by buffering of intracellular free calcium with BAPTA.
At 25 mm HCO− 3, but not in nominally HCO− 3-free medium, Na+/H+ exchange contributes significantly to regulatory volume increase in Ehrlich cells.
Under isotonic conditions, the Na+/H+ exchanger is activated by ionomycin, an effect which may be secondary to ionomycin-induced cell shrinkage.
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Received: 2 March 1995/Revised: 29 September 1995
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Pedersen, S., Kramhøft, B., Jørgensen, N. et al. Shrinkage-induced Activation of the Na+/H+ Exchanger in Ehrlich Ascites Tumor Cells: Mechanisms Involved in the Activation and a Role for the Exchanger in Cell Volume Regulation. J. Membrane Biol. 149, 141–159 (1996). https://doi.org/10.1007/s002329900015
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DOI: https://doi.org/10.1007/s002329900015