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Mitogen‐independent activation of Na + /H + exchange in human epidermoid carcinoma A431 cells: Regulation by medium osmolarity
Author(s) -
Cassel Dan,
Whiteley Brian,
Zhuang Ying Xin,
Glaser Luis
Publication year - 1985
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041220203
Subject(s) - antiporter , intracellular ph , intracellular , osmotic concentration , epidermal growth factor , biophysics , epidermoid carcinoma , a431 cells , chemistry , bicarbonate , tonicity , cell culture , biochemistry , biology , cell , membrane , cell cycle , carcinoma , genetics , receptor , molecular medicine , organic chemistry
Abstract Previous studies have documented the activation of Na + /H + exchange in A431 cells by the addition of epidermal growth factor or serum (Rothenberg et al., 1983b). Here we show that exposure of A4 31 cells to medium of increased osmolarity also leads to activation of Na + /H + exchange and to an increase in intracellular pH (pH i ), which under a variety of conditions displays similar kinetics to that observed upon addition of mitogens to the cells. Measurements of cell volume using the 3–0‐methylglucose equilibration technique clearly show that mitogens do not activate Na + /H + exchange by an osmotic mechanism (i.e., a decrease in cell volume). In fact, mitogens can induce further intracellular alkalinization if added to cells which have been shrunken in hypertonic medium. Activation of the Na + /H + antiport does not lead to an obligatory change in pH i . Addition of epidermal growth factor of hypertonic solution to A431 cells in bicarbonate buffer activates Na + /H + exchange without a concomitant increase in pH i . Under these conditions the increased proton efflux via Na + /H + exchange must therefore be compensated by other mechanisms that control cytoplasmic pH.