AJP - Cell Physiology, Vol 266, Issue 6 C1744-C1753, Copyright © 1994 by American Physiological Society

ARTICLES

Shrinkage-induced activation of Na(+)-H+ exchange in barnacle muscle fibers

B. A. Davis, E. M. Hogan and W. F. Boron
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.

We examined the effect of shrinkage on Na(+)-H+ exchange in single muscle fibers at intracellular pH (pHi) values of 6.8, 7.2, and 7.6 using pH microelectrodes and internal dialysis. Under normotonic conditions (975 mosmol/kgH2O) at pHi 6.8, the amiloride-sensitive acid-extrusion rate (JAmil/s) averaged 17 microM/min. Exposure to hypertonic solutions (1,600 mosmol/kgH2O) increased JAmil/s to 304 microM/min at pHi 6.8. At pHi approximately 7.2 and 7.6, hypertonicity increased JAmil/s from approximately 0 to approximately 172 microM/min (pHi 7.2) and approximately 0 to approximately 90 microM/min (pHi 7.6). Thus, under normotonic conditions, Na(+)-H+ exchange activity is slight at pHi approximately 6.8 and virtually nil at higher pHi values. Shrinkage stimulated Na(+)-H+ exchange, more at low pHi values. We also examined the Cl- dependence of the Na(+)-H+ exchanger's response to shrinkage. Our results indicate that shrinkage-induced activation of Na(+)-H+ exchange requires Cl-, specifically intracellular Cl-. These results establish that shrinkage is both pHi dependent and requires intracellular Cl-.

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