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Ashok K Grover

Publications and source records attributed to Ashok K Grover.

8 recordsLinked to original sources
PubMed2003

Effects of peroxynitrite on pig coronary artery smooth muscle.

We examined the effects of peroxynitrite pretreatment of pig coronary arteries on their sarcoplasmic reticulum (SR) Ca(2+) pump function. Pretreating rings from de-endothelialized arteries with peroxynitrite, followed by a wash to remove this agent, led to a decrease in the force of contraction produced in response to the SR Ca(2+) pump inhibitor cyclopiazonic acid (CPA, IC(50) = 87 +/- 6 microM). Inclusion of catalase and superoxide dismutase with the peroxynitrite did not alter its effect indicating that the inhibition was produced by peroxynitrite. Contractions produced by 30 mM KCl were not affected by up to 250 microM peroxynitrite. Smooth muscle cells cultured from this artery gave a transient increase in cytosolic Ca(2+) in response to CPA. Treating the cells with peroxynitrite inhibited this increase. Treating the SR-enriched isolated subcellular membrane fraction with peroxynitrite produced an inhibition of the ATP-dependent azide-insensitive oxalate-stimulated Ca(2+) uptake. Thus, peroxynitrite damages the SR Ca(2+)pump in the coronary artery, and this inhibition appears to lead to an inability of the arteries to respond to CPA. Thus, peroxynitrite produced from superoxide and NO in the arteries may compromise regulation of coronary tone which requires mobilization of Ca(2+) from the SR.

Adenosine Triphosphate↗
PubMed2003

Endothelium and smooth muscle of pig coronary artery: differences in metabolism.

Here, we report that the smooth muscle and endothelium of the pig coronary artery differ in the profiles of energy metabolism nucleotides. ATP levels in the freshly isolated smooth muscle (1490 +/- 93, all the values are in pmol/mg protein) were significantly greater than in the endothelium (418 +/- 68). In contrast, endothelium contained higher levels of NADH (328 +/- 21), NAD+ (1210 -/+ 28), NADPH (87 +/- 2), and NADP+ (77 +/- 4) than smooth muscle (17 +/- 2, 96 +/- 14, 7 +/- 1, and 8 +/- 1, respectively). However, smooth muscle and endothelium do not differ from each other in the ratios of NADH/NAD+ or NADPH/NADP+. Cells cultured from smooth muscle and endothelium contained less ATP (93 +/- 2, 141 +/- 6) and had lower ratios of NADH/ NAD+ than the freshly isolated tissues but the NADPH/NADP+ ratios remained similar. We conclude that (a) freshly isolated smooth muscle and endothelium differ in their profiles of the energy metabolism nucleotides, and (b) culturing the cells alters the profile.

Adenosine Triphosphate↗
PubMed2002

Peroxynitrite and nitric oxide differ in their effects on pig coronary artery smooth muscle.

Peroxynitrite generated in arteries from superoxide and nitric oxide (NO) may damage their function. Here, we compare the effects of peroxynitrite and peroxynitrite/NO-generating agents SIN-1 (3-morpholinosydnonimine hydrochloride), SNAP (S-nitroso-N-acetyl-penicillamine), SNP (sodium nitroprusside), and NONOate (spermine NONOate) on pig coronary artery. Deendothelialized artery rings were pretreated with these agents and then washed before examining their contractility. Pretreatment with all agents (200 microM) results in a decrease in the force of contraction in response to the sarco(endo)plasmic Ca(2+) (SERCA) pump inhibitor cyclopiazonic acid (CPA): SNAP > NONOate > or = peroxynitrite > or = SIN-1 > SNP. Pretreatment with SNAP, NONOate, or SIN-1 also inhibits the force of contraction produced with 30 mM KCl, with SNAP being the most potent. Including catalase plus superoxide dismutase (SOD) during the preincubation has no effect. Including an NO scavenger [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] or a guanylate cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) partially protects against SNAP. Pretreatment of cultured cells with peroxynitrite, but not with SNAP, inhibits the Ca(2+) transients produced in response to CPA. Pretreating isolated membrane vesicles with peroxynitrite inhibits the Ca(2+) uptake due to the SERCA pump, with all the other agents being less effective. Thus peroxynitrite and NO both inhibit the CPA-induced contractions in deendothelialized artery rings, peroxynitrite by damage to the SERCA pump and NO possibly by a step downstream from the increase in cytosolic Ca(2+).

Animals↗
PubMed2002

Effects of peroxynitrite on sarcoplasmic reticulum Ca2+ pump in pig coronary artery smooth muscle.

Peroxynitrite generated in arteries from superoxide and NO may damage Ca(2+) pumps. Here, we report the effects of peroxynitrite on ATP-dependent azide-insensitive uptake of Ca(2+) into pig coronary artery vesicular membrane fractions F2 [enriched in plasma membrane (PM)] and F3 [enriched in sarcoplasmic reticulum (SR)]. Membranes were pretreated with peroxynitrite and then with DTT to quench this agent. This pretreatment inhibited Ca(2+) uptake in a peroxynitrite concentration-dependent manner, but the effect was more severe in F3 than in F2. The inhibition was thus not overcome by excess DTT used to quench peroxynitrite and was not affected if catalase, SOD, or mannitol was added along with peroxynitrite. Such damage to the pump protein would be difficult to repair if produced during ischemia-reperfusion. The acylphosphates formed with ATP in F3 corresponded mainly to the SR Ca(2+) pump (110 kDa), but in F2 both PM (140 kDa) and 110-kDa bands were observed. Peroxynitrite treatment of F2 inhibited only the 110-kDa band. Inhibition of Ca(2+) uptake and acylphosphate formation from ATP correlated well in peroxynitrite-treated F3 samples. However, inhibition of acylphosphates from orthophosphate (reverse reaction of the pump) was slightly poorer. Peroxynitrite treatment also covalently cross-linked the pump protein, yielding no dimers but only larger oligomers. In contrast, cross-linking of the SR Ca(2+) pump in skeletal and cardiac muscles gives dimers as the first oligomers. Therefore, we speculate that SERCA2 has a different quaternary structure in the coronary artery smooth muscle.

Acid Anhydride Hydrolases↗
PubMed2002

Dehydroascorbic acid uptake by coronary artery smooth muscle: effect of intracellular acidification.

Dehydroascorbic acid (DHAA) enters cells via Na(+)-independent glucose transporters (GLUT) and is converted to ascorbate. However, we found that Na(+) removal inhibited [(14)C]DHAA uptake by smooth-muscle cells cultured from pig coronary artery. The uptake was examined for 2-12 min at 10-200 microM DHAA in either the presence of 134 mM Na(+) or in its absence (N-methyl D-glucamine, choline or sucrose replaced Na(+)). This inhibition of DHAA uptake by Na(+) removal was paradoxical because it was inhibited by 2-deoxyglucose and cytochalasin B, as expected of transport via the GLUT pathway. We tested the hypothesis that this paradox resulted from an inefficient intracellular reduction of [(14)C]DHAA into [(14)C]ascorbate upon intracellular acidosis caused by the Na(+) removal. Consistent with this hypothesis: (i) the Na(+)/H(+)-exchange inhibitors ethylisopropyl amiloride and cariporide also decreased the uptake, (ii) Na(+) removal and Na(+)/H(+)-exchange inhibitors lowered cytosolic pH, with the decrease being larger in 12 min than in 2 min, and (iii) less of the cellular (14)C was present as ascorbate (determined by HPLC) in cells in Na(+)-free buffer than in those in Na(+)-containing buffer. This inability to obtain ascorbate from extracellular DHAA may be detrimental to the coronary artery under hypoxia-induced acidosis during ischaemia/reperfusion.

Adenosine Triphosphate↗
PubMed2002

Sarcoplasmic reticulum Ca(2+) pump mRNA stability in cardiac and smooth muscle: role of the 3'-untranslated region.

Stomach smooth muscle (SSM) and left ventricular muscle (LVM) express the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pump gene SERCA2. Alternative splicing yields two major isoforms, SERCA2a in LVM and slow twitch muscle and SERCA2b in SSM and most other tissues. The splices have different 3'-untranslated regions (UTR) and also encode proteins that differ slightly in their COOH-terminal domains. SERCA2 transcription rates are similar in the two tissues, yet LVM has a much higher level of SERCA2 mRNA than SSM. To understand the control of SERCA2 RNA expression, we inhibited transcription and showed that the half-life of SERCA2 mRNA is significantly longer (P < 0.05) in primary cultures of LVM cells than in SSM cells. Nuclear SERCA2 mRNA levels were also higher in LVM than in SSM. In vitro decay assays using synthetic RNA corresponding to the 3'-UTR of SERCA2a and -2b showed that nuclear extracts produced a faster decay of SERCA2 RNA than cytoplasmic extracts and that nuclear extracts produced a faster decay of SERCA2b than -2a. This was also true when the full-length native mRNA was used instead of the 3'-UTR RNA, and SERCA2b decay by cytoplasmic extracts was faster for LVM than for SSM. We propose that nuclear decay is an initial step in the control of SERCA2 RNA abundance and that this control is maintained or modulated in the cytoplasm. We discuss how these control mechanisms may be part of a control switch in cardiac development and pathophysiology.

3' Untranslated Regions↗
PubMedDate not supplied

Effects of free radicals on coronary artery.

Coronary arteries supply blood to the heart and hence the control of coronary tone is pivotal to human survival. Reactive oxygen species (ROS) in specified amounts play an important role in normal metabolic and signalling processes. However, excess ROS can cause severe cardiovascular damage. For example, NO is produced by endothelium as a signal for relaxation. However, in an inflammatory response, NO from endothelium or macrophages can combine with superoxide to produce more deleterious peroxynitrite. Excess ROS have been associated with loss of coronary artery pliability--loss of contraction in some instances and relaxation in others. Atherosclerosis may also be considered an inflammatory response that leads to artery blockage, coronary disease and ischaemia-reperfusion. ROS produce various types of damage to ion channels and pumps and this damage is associated with vascular diseases such as atherosclerosis and hypertension. Endothelium and smooth muscle in the coronary artery are also affected differently by individual ROS. In fact, endothelium may act to protect the underlying smooth muscle against ROS. This review will give an overview of this field.

Cardiovascular Diseases↗