Thesis
Role of the sarcoplasmic reticulum in nitric oxide-induced modulation of cytoplasmic calcium in rabbit aortic smooth muscle cells
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2000
- Thesis identifier
- T10084
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Nitric oxide (NO) relaxes vascular smooth muscle in part by reducing cytoplasmic calcium concentration ([Ca²⁺]i). This has been proposed to be achieved by several mechanisms, including modulation of Ca2+ movements from the sarcoplasmic reticulum (SR) and activation of K+ channels. This study investigated the roles of these mechanisms in the vasodilator effect of NO in rabbit aortic smooth muscle. Caffeine and noradrenaline evoked [Ca2+]j transients due to SR Ca2+ release. These were recorded with the whole-cell, patch-clamp technique or fura-2 fluorescence. The NO donor, sodium nitroprusside (SNP) did not affect voltage-activated K+ currents, but enhanced caffeine-activated K+ currents at 1 µM, while inhibiting them at 10 µM. SNP, glyceryl trinitrate and 8-bromo-cyclic guanosine monophosphate, at concentrations causing maximal vasodilation, had no consistent effect on global [Ca2+]j or the rate of Ca2+ removal from the cell, which largely reflected Ca2+ sequestration by the SR Ca2+ - ATPase. The augmentation of caffeine-induced Ca2+ release by SNP reflected enhanced sequestration, but only in the vicinity of the plasma membrane. The reduction of the caffeine-activated [Ca2+]i transient at higher concentrations appeared to reflect inhibition of SR Ca2+ release via the ryanodine receptor. Two complementary actions of SNP on SR Ca handling, which would promote vasodilation, were therefore identified. The inhibitory effect on Ca2+ release may be mediated by guanosine 3 ’:5’-cyclic monophosphate (cGMP), because it was blocked by the cytoplasmic guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, and mimicked by a cGMP- specific (zaprinast), and a non-specific (3-isobutyl-1-methyl xanthine; IBMX) phosphodiesterase inhibitor. IBMX unexpectedly reversed the inhibitory effect of SNP, possibly by increasing levels of adenosine 3’:5’-cyclic monophosphate, which could enhance SR Ca2+ release and uptake. Since maximal vasodilation is produced below 10 µM SNP, the role of reduced Ca2+ release is unclear. However, my results support enhanced SR Ca2+ sequestration as a mechanism of nitrovasodilator action in rabbit aorta.
- Advisor / supervisor
- Gurney, Alison
- Resource Type
- DOI
- EThOS ID
- 248585
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