title: Knockout of Na+/Ca2+ exchanger in smooth muscle attenuates vasoconstriction and L-type Ca2+ channel current and lowers blood pressure.
abstract: Mice with smooth muscle (SM)-specific knockout of Na(+)/Ca(2+) exchanger type-1 (NCX1(SM-/-)) and the NCX inhibitor, SEA0400, were used to study the physiological role of NCX1 in mouse mesenteric arteries. NCX1 protein expression was greatly reduced in arteries from NCX1(SM-/-) mice generated with Cre recombinase. Mean blood pressure (BP) was 6-10 mmHg lower in NCX1(SM-/-) mice than in wild-type (WT) controls. Vasoconstriction was studied in isolated, pressurized mesenteric small arteries from WT and NCX1(SM-/-) mice and in heterozygotes with a global null mutation (NCX1(Fx/-)). Reduced NCX1 activity was manifested by a marked attenuation of responses to low extracellular Na(+) concentration, nanomolar ouabain, and SEA0400. Myogenic tone (MT, 70 mmHg) was reduced by approximately 15% in NCX1(SM-/-) arteries and, to a similar extent, by SEA0400 in WT arteries. MT was normal in arteries from NCX1(Fx/-) mice, which had normal BP. Vasoconstrictions to phenylephrine and elevated extracellular K(+) concentration were significantly reduced in NCX1(SM-/-) arteries. Because a high extracellular K(+) concentration-induced vasoconstriction involves the activation of L-type voltage-gated Ca(2+) channels (LVGCs), we measured LVGC-mediated currents and Ca(2+) sparklets in isolated mesenteric artery myocytes. Both the currents and the sparklets were significantly reduced in NCX1(SM-/-) (vs. WT or NCX1(Fx/-)) myocytes, but the voltage-dependent inactivation of LVGCs was not augmented. An acute application of SEA0400 in WT myocytes had no effect on LVGC current. The LVGC agonist, Bay K 8644, eliminated the differences in LVGC currents and Ca(2+) sparklets between NCX1(SM-/-) and control myocytes, suggesting that LVGC expression was normal in NCX1(SM-/-) myocytes. Bay K 8644 did not, however, eliminate the difference in myogenic constriction between WT and NCX1(SM-/-) arteries. We conclude that, under physiological conditions, NCX1-mediated Ca(2+) entry contributes significantly to the maintenance of MT. In NCX1(SM-/-) mouse artery myocytes, the reduced Ca(2+) entry via NCX1 may lower cytosolic Ca(2+) concentration and thereby reduce MT and BP. The reduced LVGC activity may be the consequence of a low cytosolic Ca(2+) concentration.
authors.affiliation: Department of Physiology, University of Maryland School of Medicine, 655 W. Baltimore St., Baltimore, MD 21201, USA. jzhan002@umaryland.edu
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Chongyu
authors.initials: C
authors.lastname: Ren
authors.forename: Ling
authors.initials: L
authors.lastname: Chen
authors.forename: Manuel F
authors.initials: MF
authors.lastname: Navedo
authors.forename: Laura K
authors.initials: LK
authors.lastname: Antos
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Kinsey
authors.forename: Takahiro
authors.initials: T
authors.lastname: Iwamoto
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Philipson
authors.forename: Michael I
authors.initials: MI
authors.lastname: Kotlikoff
authors.forename: Luis F
authors.initials: LF
authors.lastname: Santana
authors.forename: W Gil
authors.initials: WG
authors.lastname: Wier
authors.forename: Donald R
authors.initials: DR
authors.lastname: Matteson
authors.forename: Mordecai P
authors.initials: MP
authors.lastname: Blaustein
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000033:anatomy & histology / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D015153:Blotting, Western; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects; D004594:Electrophysiology; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009129:Muscle Tonus / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000502:physiology; D018408:Patch-Clamp Techniques; D010647:Phenyl Ethers / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000502:physiology*; D013686:Telemetry; D014661:Vasoconstriction / Q000502:physiology*
chemical_list: D000814:Aniline Compounds; D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D007202:Indicators and Reagents; D010647:Phenyl Ethers; C430918:SEA 0400; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D049452:Green Fluorescent Proteins; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester