title: Role of G proteins in stimulation of Na-H exchange by cell shrinkage.
abstract: Many cells respond to shrinkage by stimulating specific ion transport processes (e.g., Na-H exchange). However, it is not known how the cell senses this volume change, nor how this signal is transduced to an ion transporter. We have studied the activation of Na-H exchange in internally dialyzed barnacle muscle fibers, measuring intracellular pH (pHi) with glass microelectrodes. When cells are dialyzed to a pHi of approximately 7.2, Na-H exchange is active only in shrunken cells. We found that the shrinkage-induced stimulation of Na-H exchange, elicited by increasing medium osmolality from 975 to 1,600 mosmol/kgH2O, is inhibited approximately 72% by including in the dialysis fluid 1 mM guanosine 5'-O-(2-thiodiphosphate). The latter is an antagonist of G protein activation. Even in unshrunken cells, Na-H exchange is activated by dialyzing the cell with 1 mM guanosine 5'-O-(3-thiotriphosphate), which causes the prolonged activation of G proteins. Activation of Na-H exchange is also elicited in unshrunken cells by injecting cholera toxin, which activates certain G proteins. Neither exposing cells to 100 nM phorbol 12-myristate 13-acetate nor dialyzing them with a solution containing 20 microM adenosine 3',5'-cyclic monophosphate (cAMP) (or 50 microM dibutyryl cAMP) plus 0.5 mM 3-isobutyl-1-methylxanthine substantially stimulates the exchanger. Thus our data suggest that a G protein plays a key role in the transduction of the shrinkage signal to the Na-H exchanger via a pathway that involves neither protein kinase C nor cAMP.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: B A
authors.initials: BA
authors.lastname: Davis
authors.forename: E M
authors.initials: EM
authors.lastname: Hogan
authors.forename: W F
authors.initials: WF
authors.lastname: Boron
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002477:Cells / Q000166:cytology / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D009132:Muscles / Q000166:cytology / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D012016:Reference Values; D017923:Sodium-Hydrogen Exchangers; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D002772:Cholera Toxin; D000242:Cyclic AMP; D011493:Protein Kinase C; D019204:GTP-Binding Proteins