title: P2X1 receptors mediate sympathetic postjunctional Ca2+ transients in mesenteric small arteries.
abstract: Brief, spatially localized Ca(2+) transients occur in the smooth muscle adjacent to perivascular nerves of small arteries during neurogenic contractions. We named these "junctional Ca(2+) transients" (jCaTs) and postulated that they arose from Ca(2+) entering smooth muscle cells through P2X(1) receptors activated by neurally released ATP. Nevertheless, the lack of potent, subtype-selective P2X-receptor antagonists made determining the exact molecular identity of the channels difficult. Here we used small, pressurized mesenteric arteries from P2X(1)-receptor-deficient mice (KO) to test the hypothesis that jCaTs arise from Ca(2+) entering the smooth muscle cell via P2X(1) receptors. In wild-type (WT) arteries, confocal microscopy of fluo-4 fluorescence during electrical field stimulation (EFS) of perivascular sympathetic nerves revealed jCaTs in the smooth muscle cells adjacent to the perivascular nerves, similar to those reported previously in rat arteries, and alpha-latrotoxin (2.5 nM) markedly increased the frequency of "spontaneous" jCaTs. In the KO arteries, however, neither EFS nor alpha-latrotoxin elicited any jCaTs. A potent P2X-receptor agonist, alpha,beta-methylene ATP (10.0 microM), elicited strong contractions and increased intracellular Ca(2+) concentration in WT arteries but elicited neither in KO arteries. A biphasic vasoconstriction in response to EFS was observed in WT arteries. In KO arteries, however, the initial rapid, transient component of the biphasic vasoconstriction was absent. The data support the hypothesis that jCaTs represent Ca(2+) that enters the smooth muscle cells through P2X(1) receptors activated by neurally released ATP and that this Ca(2+) is involved in the initial rapid component of the sympathetic neurogenic contraction.
authors.affiliation: Department of Physiology, University of Maryland, Baltimore, MD 21201, USA. clamo001@umaryland.edu
authors.forename: Christine
authors.initials: C
authors.lastname: Lamont
authors.forename: C
authors.initials: C
authors.lastname: Vial
authors.forename: R J
authors.initials: RJ
authors.lastname: Evans
authors.forename: W G
authors.initials: WG
authors.lastname: Wier
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D008638:Mesenteric Arteries / Q000294:innervation* / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009131:Muscle, Smooth, Vascular / Q000294:innervation* / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000502:physiology; D011224:Prazosin / Q000494:pharmacology; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058469:Receptors, Purinergic P2X; D013111:Spider Venoms / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology
chemical_list: D000959:Antihypertensive Agents; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D013111:Spider Venoms; C020763:alpha-latrotoxin; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium; D011224:Prazosin