title: Effect of nitric oxide donors and noradrenaline on Ca2+ release sites and global intracellular Ca2+ in myocytes from guinea-pig small mesenteric arteries.
abstract: In smooth muscle the spontaneous Ca2+ release from the sarcoplasmic reticulum (SR) occurs at preferred locations called frequent discharge sites (FDSs) giving rise to localized intracellular Ca2+ transients (Ca2+ sparks). Laser scanning confocal microscopy of fluo-3-loaded single myocytes freshly isolated from small mesenteric arteries of guinea-pig was used to investigate the action of nitric oxide (NO) donors and noradrenaline on the position and activity of FDSs and on global intracellular Ca2+ concentration ([Ca2+]i). In 8 % of cells 'microsparks', Ca2+ release events smaller in duration, spread and amplitude than Ca2+ sparks were observed. The location of the initiation point of Ca2+ sparks observed during line-scan imaging was found to 'jitter' by +/- 0.41 microm. However, the general position of an FDS within the cell did not change; most FDSs were close (within 1.2 +/- 0.1 microm) to the cell membrane and often multiple FDSs occurred in one confocal plane of the cell. In the resting state, NO donors S-nitroso-N-acetylpenicillamine (SNAP; 50 microM) and sodium nitroprusside (SNP; 100 microM) did not change the general position of FDSs and slightly depressed their activity, but did not affect the global [Ca2+]i significantly. Application of noradrenaline (1-10 microM) increased Ca2+ spark frequency at existing FDS(s) leading to a Ca2+ wave. The increase in FDS activity and in global [Ca2+]i produced by noradrenaline were inhibited by the presence of SNAP or SNP but not by 8-bromoguanosine cyclic 3',5'-monophosphate (8-Br-cGMP; 100 microM). In the presence of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), inhibitor of soluble guanylate cyclase, SNAP and SNP still exerted their effects on the noradrenaline response. These results suggest that SNAP and SNP inhibit the noradrenaline-evoked rise in global [Ca2+]i by a cGMP-independent mechanism and that part of this effect is due to inhibition of the activity of FDSs; moreover, only the activity, but not the position, of FDSs is changed by either stimulant or inhibitory substances.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK. v.pucovsky@sghms.ac.uk
authors.forename: Vladimír
authors.initials: V
authors.lastname: Pucovský
authors.forename: Dmitri V
authors.initials: DV
authors.lastname: Gordienko
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Bolton
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000502:physiology; D006168:Guinea Pigs; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D008638:Mesenteric Arteries / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D026423:S-Nitroso-N-Acetylpenicillamine / Q000494:pharmacology
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D010069:Oxadiazoles; D011810:Quinoxalines; D009599:Nitroprusside; C016276:8-bromocyclic GMP; D026423:S-Nitroso-N-Acetylpenicillamine; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D002118:Calcium; D009638:Norepinephrine