Shrinkage-induced activation of Na(+)-H+ exchange in barnacle muscle fibers.
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-.
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
B A
BA
Davis
E M
EM
Hogan
W F
WF
Boron
D000818:Animals; D002712:Chlorides / Q000494:pharmacology; D003956:Dialysis; D006863:Hydrogen-Ion Concentration; D006982:Hypertonic Solutions / Q000494:pharmacology; D008839:Microelectrodes; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D001468:Thoracica
D002712:Chlorides; D006982:Hypertonic Solutions; D017923:Sodium-Hydrogen Exchangers