Biomedical subjects

Stephen T O'Rourke

Publications and source records attributed to Stephen T O'Rourke.

5 recordsLinked to original sources

PubMed2006

Sirolimus causes relaxation of human vascular smooth muscle: a novel action of sirolimus mediated via ATP-sensitive potassium channels.

Little is known about the vasomotor effects of sirolimus, and preliminary studies using animal models have provided conflicting results. The present study was designed to determine the effects of sirolimus on vasomotor tone in human blood vessels. Human radial artery segments were cut into rings, denuded of endothelium, and placed into organ chambers for isometric tension recording. Sirolimus (10(-10) to 10(-6) M) caused concentration-dependent relaxation of human arteries contracted with U46619 (9,11-dideoxy-11alpha,9alpha-epoxymethano-prostaglandin F(2alpha); 10(-8) M) [-log (M) EC(50) (pD(2)) = 7.28 +/- 0.1; E(max) = 57 +/- 6%] or phenylephrine (10(-6) M) (pD(2) = 7.16 +/- 0.4; E(max) = 45 +/- 9%). Sirolimus-induced relaxation was unaffected by treatment with indomethacin (10(-5) M) but was nearly abolished in tissues contracted by depolarization with elevated K(+) (60 mM). In U46619-contracted rings, the response to sirolimus was markedly inhibited in the presence of the specific ATP-sensitive potassium (K(ATP)) channel blocker, glyburide (10(-6) M), but was unaffected by treatment with blockers of large conductance, calcium-activated potassium channel (iberiotoxin, 10(-7) M), small conductance, calcium-activated potassium channel (apamin, 10(-6) M), or voltage-gated potassium channel (4-aminopyridine, 10(-3) M). The K(ATP) channel opener, aprikalim (10(-7) to 10(-5) M), caused concentration-dependent relaxations that were inhibited by glyburide (10(-6) M) and abolished in tissues contracted with elevated K(+) (60 mM), thus confirming that K(ATP) channel opening causes relaxation of these arteries. These data suggest that sirolimus, at concentrations attained in vivo, causes relaxation of human arteries, and this effect is mediated by opening of K(ATP) channels in vascular smooth muscle. Reduced vasomotor tone is a heretofore unrecognized action of sirolimus that could potentially contribute to its efficacy in drug-eluting stents.

Adenosine Triphosphate↗

PubMed2006

Role of endogenous hydrogen peroxide in the development of nitrate tolerance.

The present study was designed to test the hypothesis that hydrogen peroxide plays a role in the development of nitrate tolerance. Isolated rat aortic rings were suspended in organ chambers for isometric tension recording. The rings were incubated with (tolerant) and without (control) nitroglycerin (10(-4) M) for 90 min, followed by repeated rinsing for 1 h. Hydrogen peroxide release in control and tolerant tissues was measured fluorimetrically using amplex red. Nitroglycerin (10(-9)-10(-4) M) caused concentration-dependent relaxations in control (-logEC50=7.15+/-0.1) and tolerant rings (-logEC50=5.83+/-0.1) contracted with norepinephrine. Nitrate tolerance was evident by a >20-fold rightward shift in the nitroglycerin concentration-response curve in tissues exposed previously to nitroglycerin for 90 min. Incubation of the rings with the superoxide dismutase (SOD)-mimetic, tempol (10(-4) M), during the 90-min exposure period to nitroglycerin caused a leftward shift in the nitroglycerin concentration-response curve in tolerant rings (-logEC50=6.84+/-0.2), but had no effect on the response to nitroglycerin in control rings. Treatment of the rings with catalase (1200 U/ml) or ebselen (1.5x10(-5) M), a glutathione peroxidase-mimetic, during the 90-min exposure period to nitroglycerin resulted in a further rightward shift in the nitroglycerin concentration-response curve in tolerant rings (-logEC50=5.41+/-0.1 and 4.98+/-0.1; catalase and ebselen respectively), without altering the response to nitroglycerin in control rings. In the presence of catalase, the effect of tempol on nitrate tolerance was abolished (-logEC50=5.46+/-0.1). Hydrogen peroxide release was reduced by approximately 64% in nitrate tolerant tissues when compared to control. The decrease in hydrogen peroxide release was completely reversed by treatment with tempol, whereas treatment with ebselen caused a further decrease in hydrogen peroxide release in nitrate tolerant tissues. Addition of hydrogen peroxide (3x10(-5) M) to nitrate tolerant rings caused a leftward shift in the nitroglycerin concentration-response curve in tolerant rings (-logEC50=7.18+/-0.3), but had no effect on the response to nitroglycerin in control rings. These results suggest that nitrate tolerance is associated with decreased endogenous formation of hydrogen peroxide, which attenuates nitrate tolerance development. SOD-mimetics may reduce nitrate tolerance, in part, by increasing the formation of hydrogen peroxide.

Animals↗

PubMed2006

Nitroglycerin-induced release of calcitonin gene-related peptide from sensory nerves attenuates the development of nitrate tolerance.

The present study was designed to determine if endogenous calcitonin gene-related peptide (CGRP) affects the process of nitrate tolerance development in blood vessels. Rat aortic rings were suspended in organ chambers and relaxations to nitroglycerin (10(-9) -10(-6) M) were obtained in nitrate tolerant and nontolerant rings contracted with norepinephrine (10(-7) M). Tolerance was induced by incubating the rings with (tolerant) or without (nontolerant) nitroglycerin (10(-4) M) for 90 minutes, followed by repeated rinsing for 1 hour. Some rings were treated with CGRP8-37 (10(-6) M), glyburide (10(-6) M), or iberiotoxin (10(-7) M) during the 90-minute desensitization period with nitroglycerin (10(-4) M), and were then washed out during the 1-hour rinsing period. Other rings were treated with capsaicin (10(-5) M) prior to the 90-minute desensitization period. Calcitonin gene-related peptide release was measured by radioimmunoassay. Relaxation to nitroglycerin was markedly reduced in tolerant rings, as compared with nontolerant. Incubation with CGRP8-37 (10(-6) M) specifically during the 90-minute desensitization period with nitroglycerin resulted in even greater impairment in the response to nitroglycerin in tolerant rings, even though the calcitonin gene-related peptide antagonist had been washed out before completion of the nitroglycerin dose-response curve. Similar results were obtained following depletion of calcitonin gene-related peptide stores in sensory nerves by treatment with capsaicin (10(-5) M) prior to the 90-minute desensitization period with nitroglycerin. Prior treatment with CGRP8-37 or capsaicin had no effect on the response to nitroglycerin in nontolerant rings. Incubation with glyburide (10(-6) M), but not iberiotoxin (10(-7) M), specifically during the 90-minute desensitization period, mimicked the effect of CGRP8-37 and capsaicin in tolerant rings, suggesting a role for KATP channels in the effect of calcitonin gene-related peptide. Nitroglycerin (10(-4) M) caused a greater than twofold increase over basal levels in calcitonin gene-related peptide release in nontolerant rings, which was abolished in rings treated with capsaicin and in nitrate tolerant rings. These results suggest that nitroglycerin releases calcitonin gene-related peptide from sensory nerves during the process of desensitization to nitrovasodilators, and that interference with either the release or action of endogenous calcitonin gene-related peptide during this period enhances the extent to which nitrate tolerance occurs. The finding that nitroglycerin-induced release of calcitonin gene-related peptide from sensory nerves attenuates the desensitizing effect of nitroglycerin represents a heretofore unknown event in the development of nitrate tolerance, and demonstrates a novel role for calcitonin gene-related peptide in the vasculature.

Animals↗

PubMed2005

Large-conductance, calcium-activated potassium channels: structural and functional implications.

The large-conductance, calcium-activated potassium channels (BK, also termed BK(Ca), Slo, or MaxiK) distributed in both excitable and non-excitable cells are involved in many cellular functions such as action potential repolarization; neuronal excitability; neurotransmitter release; hormone secretion; tuning of cochlear hair cells; innate immunity; and modulation of the tone of vascular, airway, uterine, gastrointestinal, and urinary bladder smooth muscle tissues. Because of their high conductance, activation of BK channels has a strong effect on membrane potential. BK channels differ from all other potassium (K(+)) channels due to their high sensitivity to both intracellular calcium (Ca(2+)) concentrations and voltage. These features make BK channels ideal negative feedback regulators in many cell types by decreasing voltage-dependent Ca(2+) entry through membrane potential hyperpolarization. The current review aims to give a comprehensive understanding of the structure and molecular biology of BK channels and their relevance to various pathophysiological conditions. The review will also focus on the therapeutic potential and pharmacology of the various BK channel activators and blockers.

Animals↗

PubMed2003

Melatonin inhibits nitrate tolerance in isolated coronary arteries.

(1) The present study was designed to test the hypothesis that melatonin inhibits nitrate tolerance in coronary arteries. (2) Rings of porcine coronary arteries were suspended in organ chambers for isometric tension recording. Nitrate tolerance was induced by incubating the tissues with nitroglycerin (10(-4) M) for 90 min, followed by repeated rinsing for 1 h. Control rings that had not been exposed previously to nitroglycerin, but were otherwise treated identically, were studied simultaneously. The rings were contracted with U46619 (1-3 x 10(-9) M) and concentration-response curves to nitroglycerin (10(-9)-10(-4) M) were obtained. (3) Nitrate tolerance was evident by a 15- to 20-fold rightward shift in the concentration-response curve to nitroglycerin in rings with and without endothelium exposed previously to the drug for 90 min. Addition of melatonin (10(-9)-10(-7) M) to the organ chamber during the 90-min incubation period with nitroglycerin partially inhibited nitrate tolerance in coronary arteries with intact endothelium; however, melatonin had no effect on nitrate tolerance in coronary arteries without endothelium. (4) The effect of melatonin on nitrate tolerance in coronary arteries with endothelium was abolished by the melatonin receptor antagonist, S20928 (10(-6) M). In contrast to melatonin, the selective MT(3)-melatonin receptor agonist, 5-MCA-NAT (10(-8)-10(-7) M), had no effect on nitrate tolerance in coronary arteries. (5) The results demonstrate that melatonin, acting via specific melatonin receptors, inhibits nitrate tolerance in coronary arteries and that this effect is dependent on the presence of the vascular endothelium.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗