title: Cyclic GMP inhibits a pharmacologically distinct Na+/H+ exchanger variant in cultured rat astrocytes via an extracellular site of action.
abstract: There is growing evidence that cyclic GMP (cGMP) plays important roles in the brain. In cultured rat astrocytes, we observed that the cGMP-inducing C-type natriuretic peptide (CNP) and cGMP analogues caused a decrease in intracellular pH (pHi). To examine whether this effect was due to inhibition of an Na+/H+ exchanger (NHE), we acidified cells by replacing extracellular Na+ by choline and examined the kinetics of the pHi recovery that occurred on reintroduction of Na+ in the extracellular medium. Both CNP and amiloride analogues inhibited the Na(+)-dependent pHi recovery, even in the nominal absence of CO2/HCO3-. This indicated that CNP inhibited the activity of an exchanger that was Na(+)-dependent, HCO3(-)-independent, and sensitive to known inhibitors of NHE. However, comparison of the potencies of four distinct amiloride analogues revealed a pharmacological profile that was different from that of any other NHE characterized to date. cGMP mimicked the effect of CNP on sodium-dependent pHi recovery, but the native nucleotide was as potent as membrane-permeant analogues. Intracellularly produced cGMP was very rapidly exported out of astrocytes. Probenecid and niflumic acid slowed down the rate of cGMP egression and inhibited the effect of CNP on Na(+)-dependent recovery, but not that of extracellular cGMP. Altogether, our data indicate that cGMP inhibits a novel type of NHE in astrocytes via an extracellular site of action. If these results with primary cultures transfer to brain, this phenomenon may constitute a mechanism by which natriuretic peptides exert some of their actions in the brain, as pHi transients have been shown to modulate several important astrocytic functions.
authors.affiliation: Experimental Hypertension Laboratory, Institut de Recherches Cliniques de Montréal, Québec, Canada.
authors.forename: R M
authors.initials: RM
authors.lastname: Touyz
authors.forename: S
authors.initials: S
authors.lastname: Picard
authors.forename: E L
authors.initials: EL
authors.lastname: Schiffrin
authors.forename: C F
authors.initials: CF
authors.lastname: Deschepper
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D002478:Cells, Cultured / Q000187:drug effects / Q000201:enzymology; D002794:Choline / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology*; D004232:Diuretics / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D020098:Natriuretic Peptide, C-Type; D009544:Niflumic Acid / Q000494:pharmacology; D018697:Nootropic Agents / Q000494:pharmacology; D011339:Probenecid / Q000494:pharmacology; D011506:Proteins / Q000494:pharmacology; D051381:Rats; D012076:Renal Agents / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D004232:Diuretics; D018697:Nootropic Agents; D011506:Proteins; D012076:Renal Agents; D017923:Sodium-Hydrogen Exchangers; D020098:Natriuretic Peptide, C-Type; D009544:Niflumic Acid; D000584:Amiloride; D009320:Atrial Natriuretic Factor; D012964:Sodium; D006152:Cyclic GMP; D002794:Choline; D011339:Probenecid