title: Intravascular pressure augments cerebral arterial constriction by inducing voltage-insensitive Ca2+ waves.
abstract: This study examined whether elevated intravascular pressure stimulates asynchronous Ca(2+) waves in cerebral arterial smooth muscle cells and if their generation contributes to myogenic tone development. The endothelium was removed from rat cerebral arteries, which were then mounted in an arteriograph, pressurized (20-100 mmHg) and examined under a variety of experimental conditions. Diameter and membrane potential (V(M)) were monitored using conventional techniques; Ca(2+) wave generation and myosin light chain (MLC(20))/MYPT1 (myosin phosphatase targeting subunit) phosphorylation were assessed by confocal microscopy and Western blot analysis, respectively. Elevating intravascular pressure increased the proportion of smooth muscle cells firing asynchronous Ca(2+) waves as well as event frequency. Ca(2+) wave augmentation occurred primarily at lower intravascular pressures (<60 mmHg) and ryanodine, a plant alkaloid that depletes the sarcoplasmic reticulum (SR) of Ca(2+), eliminated these events. Ca(2+) wave generation was voltage insensitive as Ca(2+) channel blockade and perturbations in extracellular [K(+)] had little effect on measured parameters. Ryanodine-induced inhibition of Ca(2+) waves attenuated myogenic tone and MLC(20) phosphorylation without altering arterial V(M). Thapsigargin, an SR Ca(2+)-ATPase inhibitor also attenuated Ca(2+) waves, pressure-induced constriction and MLC(20) phosphorylation. The SR-driven component of the myogenic response was proportionally greater at lower intravascular pressures and subsequent MYPT1 phosphorylation measures revealed that SR Ca(2+) waves facilitated pressure-induced MLC(20) phosphorylation through mechanisms that include myosin light chain phosphatase inhibition. Cumulatively, our findings show that mechanical stimuli augment Ca(2+) wave generation in arterial smooth muscle and that these transient events facilitate tone development particularly at lower intravascular pressures by providing a proportion of the Ca(2+) required to directly control MLC(20) phosphorylation.
authors.affiliation: Hotchkiss Brain Institute, Libin Cardiovascular Institute, Department of Physiology & Pharmacology, University of Calgary, Alberta, Canada.
authors.forename: Rania E
authors.initials: RE
authors.lastname: Mufti
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Brett
authors.forename: Cam Ha T
authors.initials: CH
authors.lastname: Tran
authors.forename: Rasha
authors.initials: R
authors.lastname: Abd El-Rahman
authors.forename: Yana
authors.initials: Y
authors.lastname: Anfinogenova
authors.forename: Ahmed
authors.initials: A
authors.lastname: El-Yazbi
authors.forename: William C
authors.initials: WC
authors.lastname: Cole
authors.forename: Peter P
authors.initials: PP
authors.lastname: Jones
authors.forename: S R Wayne
authors.initials: SR
authors.lastname: Chen
authors.forename: Donald G
authors.initials: DG
authors.lastname: Welsh
mesh_terms: D000792:Angiography; D000818:Animals; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002536:Cerebral Arteries / Q000187:drug effects / Q000502:physiology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology*; D009213:Myography; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D012433:Ryanodine; D019284:Thapsigargin