title: Activation of the Na(+)-H+ exchanger modulates angiotensin II-stimulated Na(+)-dependent Mg2+ transport in vascular smooth muscle cells in genetic hypertension.
abstract: This study investigated the role of the Na(+)-H+ exchanger (NHE) on angiotensin II (Ang II)-induced activation of Na(+)-dependent Mg2+ transport in vascular smooth muscle cells (VSMCs) from Wistar-Kyoto rats (WKY; n=20) and spontaneously hypertensive rats (SHR; n=20). Intracellular free concentrations of Mg2+ ([Mg2+]i) and Na+ ([Na+]i) and intracellular pH (pHi) were measured with the specific fluorescent probes mag-fura 2-AM, SBFI-AM, and BCECF-AM, respectively. Na+ dependency of Mg2+ transport was assessed in Na(+)-free buffer, and the role of the NHE was determined with the highly selective NHE blocker 5-(N-methyl-N-isobutyl) amiloride (MIA). Basal [Mg2+]i was lower in SHR than WKY (0.59+/-0.01 versus 0.71+/-0.01 mmol/L, P<0.05). Basal pHi and [Na+]i were not different between the 2 groups. Ang II dose dependently increased [Na+]i and pHi and decreased [Mg2+]i. Responses were significantly greater (P<0.05) in SHR versus WKY ([Na+]i E(max)=37.5+/-1.1 versus 33.7+/-1.9 mmol/L; pHi E(max)=7.35+/-0.04 versus 7.20+/-0.01; [Mg2+]i E(min)=0. 28+/-0.09 versus 0.53+/-0.02 mmol/L, SHR versus WKY). In Na(+)-free buffer, Ang II-elicited [Mg2+]i responses were inhibited. MIA (1 micromol/L) inhibited Ang II-stimulated responses in WKY and normalized responses in SHR ([Mg2+]i E(min)=0.49+/-0.02). Ang II-stimulated activation of NHE was significantly increased (P<0.05) in SHR (0.07+/-0.002 DeltapH(i)/s) compared with WKY (0.05+/-0.004 DeltapH(i)/s). These data demonstrate that in VSMCs [Mg2+]i regulation is Na+ dependent, that activation of NHE modulates Na(+)-Mg2+ transport, and that increased activity of NHE may play a role in altered Na(+)-dependent regulation of [Mg2+]i in SHR.
authors.affiliation: Multidisciplinary Research Group on Hypertension, Clinical Research Institute of Montreal, University of Montreal, Quebec, Canada. touyzr@ircm.qc.ca
authors.forename: R M
authors.initials: RM
authors.lastname: Touyz
authors.forename: E L
authors.initials: EL
authors.lastname: Schiffrin
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D006863:Hydrogen-Ion Concentration; D006973:Hypertension / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: D017923:Sodium-Hydrogen Exchangers; D000804:Angiotensin II; D000584:Amiloride; C056369:5-(N-methyl-N-isobutyl)amiloride; D012964:Sodium; D008274:Magnesium