Nitric oxide suppresses cerebral vasomotion by sGC-independent effects on ryanodine receptors and voltage-gated calcium channels.
OBJECTIVE
In cerebral arteries, nitric oxide (NO) release plays a key role in suppressing vasomotion. Our aim was to establish the pathways affected by NO in rat middle cerebral arteries.


METHODS
In isolated segments of artery, isometric tension and simultaneous measurements of either smooth muscle membrane potential or intracellular [Ca(2+)] ([Ca(2+)](SMC)) changes were recorded.


RESULTS
In the absence of L-NAME, asynchronous propagating Ca(2+) waves were recorded that were sensitive to block with ryanodine, but not nifedipine. L-NAME stimulated pronounced vasomotion and synchronous Ca(2+) oscillations with close temporal coupling between membrane potential, tone and [Ca(2+)](SMC). If nifedipine was applied together with L-NAME, [Ca(2+)](SMC) decreased and synchronous Ca(2+) oscillations were lost, but asynchronous propagating Ca(2+) waves persisted. Vasomotion was similarly evoked by either iberiotoxin, or by ryanodine, and to a lesser extent by ODQ. Exogenous application of NONOate stimulated endothelium-independent hyperpolarization and relaxation of either L-NAME-induced or spontaneous arterial tone. NO-evoked hyperpolarization involved activation of BK(Ca) channels via ryanodine receptors (RYRs), with little involvement of sGC. Further, in whole cell mode, NO inhibited current through L-type voltage-gated Ca(2+) channels (VGCC), which was independent of both voltage and sGC.


CONCLUSIONS
NO exerts sGC-independent actions at RYRs and at VGCC, both of which normally suppress cerebral artery myogenic tone.
Yuill
Kathryn H
KH
Department of Pharmacy and Pharmacology, University of Bath, Bath.
McNeish
Alister J
AJ
Department of Pharmacy and Pharmacology, University of Bath, Bath.
Kansui
Yasuo
Y
Department of Pharmacy and Pharmacology, University of Bath, Bath.
Garland
Christopher J
CJ
Department of Pharmacology, University of Oxford, Oxford, UK.
Dora
Kim A
KA
Department of Pharmacology, University of Oxford, Oxford, UK.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D020768:Middle Cerebral Artery / Q000201:enzymology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D000071756:Soluble Guanylyl Cyclase; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D051036:Large-Conductance Calcium-Activated Potassium Channels; D020030:Nitric Oxide Donors; D026902:Potassium Channel Blockers; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; D002118:Calcium