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Effect of nitric oxide donors and noradrenaline on Ca 2+ release sites and global intracellular Ca 2+ in myocytes from guinea‐pig small mesenteric arteries
Author(s) -
Pucovský Vladimír,
Gordienko Dmitri V.,
Bolton Thomas B.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.012978
Subject(s) - biophysics , intracellular , myocyte , chemistry , nitric oxide , ryanodine receptor , sodium nitroprusside , ion transporter , snap , biochemistry , endocrinology , biology , membrane , computer graphics (images) , organic chemistry , computer science
In smooth muscle the spontaneous Ca 2+ release from the sarcoplasmic reticulum (SR) occurs at preferred locations called frequent discharge sites (FDSs) giving rise to localized intracellular Ca 2+ transients (Ca 2+ 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 Ca 2+ concentration ([Ca 2+ ] i ). In 8% of cells ‘microsparks’, Ca 2+ release events smaller in duration, spread and amplitude than Ca 2+ sparks were observed. The location of the initiation point of Ca 2+ sparks observed during line‐scan imaging was found to ‘jitter’ by ± 0.41 μm. However, the general position of an FDS within the cell did not change; most FDSs were close (within 1.2 ± 0.1 μm) 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 μ m ) and sodium nitroprusside (SNP; 100 μ m ) did not change the general position of FDSs and slightly depressed their activity, but did not affect the global [Ca 2+ ] i significantly. Application of noradrenaline (1–10 μ m ) increased Ca 2+ spark frequency at existing FDS(s) leading to a Ca 2+ wave. The increase in FDS activity and in global [Ca 2+ ] 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 μ m ). 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 [Ca 2+ ] 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.