Activation of voltage-independent Ca2+ entry by noradrenaline involves cGMP in vascular myocytes.
Stimulation of portal vein myocytes with noradrenaline (NA) in the presence of a voltage-dependent Ca2+ channel blocker, evoked a transient increase in the concentration of free cytosolic Ca2+, due to inositol 1,4,5-trisphosphate mediated Ca2+ release, followed by activation of a Ca2+ entry pathway. Combining patch-clamp and indo-1 measurements we have tested the effects of various pharmacological agents on this Ca2+ entry following NA-induced Ca2+ release in order to determine the mechanism involved. Only the guanylate cyclase inhibitor LY-83583 specifically inhibited the maintained Ca2+ entry during NA stimulation. This inhibition was reversed by dibutyryl cGMP (DB-cGMP) or 8-bromo cGMP. Under control conditions, addition of DB-cGMP to the external solution was without effect. Thapsigargin and caffeine each depleted the intracellular Ca2+ store but did not evoke Ca2+ entry in venous myocytes under control conditions. However, application of DB-cGMP or NA after Ca2+ store depletion induced by caffeine or thapsigargin caused a rise in [Ca2+]i by activation of a Ca2+ entry pathway. The effect of cGMP seems to involve phosphorylation since cGMP-activated protein kinase inhibitors KT-5823 and H-8 blocked the NA-induced Ca2+ entry. Our results thus suggest that the activation of the voltage-independent Ca2+ entry by NA involves an increase in cellular cGMP.
Grégoire
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Laboratoire de Physiologie, Faculté de médecine Victor Pachon, Université de Bordeaux II, France.
Pacaud
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Loirand
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D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000925:Anticoagulants / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D004464:Econazole / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D019833:Genistein; D006493:Heparin / Q000494:pharmacology; D015640:Ion Channel Gating / Q000502:physiology; D007529:Isoflavones / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology*; D019319:Okadaic Acid; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011169:Portal Vein / Q000166:cytology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D000634:Aminoquinolines; D000903:Antibiotics, Antineoplastic; D000925:Anticoagulants; D000935:Antifungal Agents; D002120:Calcium Channel Agonists; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D007529:Isoflavones; D010726:Phosphodiesterase Inhibitors; D013566:Sympathomimetics; D013729:Terpenes; D019319:Okadaic Acid; D003995:Dibutyryl Cyclic GMP; D002110:Caffeine; D019284:Thapsigargin; D004464:Econazole; D004317:Doxorubicin; D006493:Heparin; C041715:6-anilino-5,8-quinolinedione; D012964:Sodium; D019833:Genistein; D006152:Cyclic GMP; D002118:Calcium; D009638:Norepinephrine