Mg2+ blocks myogenic tone but not K+-induced constriction: role for SOCs in small arteries.
The effects of Mg(2+) and nifedipine (Nif) on vasoconstriction and Ca(2+) transients were studied in intact, pressurized rat mesenteric arteries with myogenic tone. Changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) were measured with confocal microscopy in fluo 4-AM loaded, individual myocytes. Myogenic tone was abolished by 10 mM Mg(2+) or 0.3 microM Nif. Contractions induced by 75 mM K(+) depolarization were blocked by 0.3 microM Nif, but not by 10 mM Mg(2+). Phenylephrine (PE; 5 microM) evoked sustained [Ca(2+)](cyt) elevation and vasoconstriction with superimposed Ca(2+) oscillations and vasomotion. The subsequent addition of 10 mM Mg(2+) or 0.3 microM Nif reduced [Ca(2+)](cyt) and abolished plateau vasoconstriction. When added before PE, both Mg(2+) and Nif abolished the PE-evoked Ca(2+) oscillations and vasomotion. Mg(2+) dilated the PE-constricted arteries after a brief (< or =180-240 s) vasoconstriction, but Nif did not. Both agents also abolished the vasoconstriction attributed to Ca(2+) entry through store-operated channels (SOCs) during internal Ca(2+) store refilling that followed store depletion. The data suggest that Ca(2+) entry through SOCs helps maintain both myogenic tone and alpha(1)-adrenoceptor-induced tonic vasoconstriction.
Zhang
Jin
J
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA.
Wier
W Gil
WG
Blaustein
Mordecai P
MP
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009129:Muscle Tonus / Q000187:drug effects* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D015220:Calcium Channels; D005456:Fluorescent Dyes; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D008274:Magnesium; D009543:Nifedipine; D011188:Potassium; D002118:Calcium