Inhibitory Effects Of Pinacidil Research Articles

Physiological function and molecular composition of ATP-sensitive K+ channels in human gastric smooth muscle.

Gastric motility is controlled by slow waves. In general, the activation of the ATP-sensitive K+ (KATP) channels in the smooth muscle opposes the membrane excitability and produces relaxation. Since metabolic inhibition and/or diabetes mellitus are accompanied by dysfunctions of gastric smooth muscle, we examined the possible roles of KATP channels in human gastric motility. We used human gastric corpus and antrum smooth muscle preparations and recorded the mechanical activities with a conventional contractile measuring system. We also identified the subunits of the KATP channels using Western blot. Pinacidil (10 μM), a KATP channel opener, suppressed contractions to 30% (basal tone to −0.2 g) of the control. The inhibitory effect of pinacidil on contraction was reversed to 59% of the control by glibenclamide (20 μM), a KATP channel blocker. The relaxation by pinacidil was not affected by a pretreatment with L-arginine methyl ester, tetraethylammonium, or 4-aminopyridine. Pinacidil also inhibited the acetylcholine (ACh)-induced tonic and phasic contractions in a glibenclamide-sensitive manner (42% and 6% of the control, respectively). Other KATP channel openers such as diazoxide, cromakalim and nicorandil also inhibited the spontaneous and ACh-induced contractions. Calcitonin gene-related peptide (CGRP), a gastric neuropeptide, induced muscle relaxation by the activation of KATP channels in human gastric smooth muscle. Finally, we have found with Western blot studies, that human gastric smooth muscle expressed KATP channels which were composed of Kir 6.2 and SUR2B subunits.

Roles of ATP sensitive potassium channel in modulating gastric tone and accommodation in dogs

Objective: The ATP sensitive potassium (KATP) channel plays an important role in the regulation of resting membrane potential and membrane excitability. The role of the KATP channel in modulating gastric motility is unclear. The aim of this study was to investigate the role and mechanism of the KATP channel in modulating gastric tone and accommodation in dogs.Materials and methods: Gastric volume under a constant pressure reflecting gastric tone was measured using a barostat device in dogs equipped with a gastric cannula. Gastric accommodation was evaluated by the difference in gastric volume before and after a liquid meal. The roles of cholinergic and nitrergic pathways in the inhibitory effect of pinacidil (a KATP opener) were assessed.Results: 1) Pinacidil dose-dependently decreased gastric tone at a dosage of 30 (p = 0.628), 100 (p = 0.013) and 300 μg kg−1 (p < 0.001). 2) Glibenclamide, a KATP blocker, completely blocked the inhibitory effect of pinacidil on gastric tone. 3) Atropine did not block the inhibitory effect of pinacidil on gastric tone but Nω-Nitro-L-arginine methyl ester markedly attenuated the inhibitory effect of pinacidil (p = 0.004). 4) Glibenclamide significantly reduced gastric accommodation (p < 0.001) while pinacidil had no effects on gastric accommodation. 5) Glibenclamide significantly reduced nitric oxide donor sodium nitroprusside-induced gastric relaxation.Conclusions: These findings indicate that the KATP channel plays an important role in modulating gastric tone and accommodation in dogs. The inhibitory effect of pinacidil on gastric tone was through the nitrergic pathway as well as acting directly on smooth muscle cells.

Effect of potassium channel opener pinacidil on the contractions elicited electrically or by noradrenaline in the human radial artery

In order to discover an agent that can prevent spasm of the human radial artery, the aim of our study was to evaluate the effect of the K + channel opener, pinacidil, on contractions in the radial artery. Contractions of the radial artery were evoked by exogenously applied noradrenaline or by electrical field stimulation (EFS, 20 Hz, neurogenic). Pinacidil induced concentration-dependent inhibition of both EFS- and noradrenaline-evoked contractions of the radial artery. Glibenclamide, a selective blocker of ATP-sensitive K + channels (Kir6.x containing subunit) antagonized in the same manner the pinacidil-induced inhibition of neurogenic contractions and contractions evoked by exogenous noradrenaline. The inhibition of pinacidil relaxation by tetraethylammonium (TEA), a blocker of Ca-sensitive K + (K Ca) channels, was more pronounced in EFS-contracted preparations. A blocker of voltage-sensitive K + (K V) channels, 4-aminopyridine (4-AP), inhibited pinacidil relaxation only in EFS-contracted preparations. In order to test the presence of different K + channels, immunohistochemistry of K + channels expression in the radial artery was performed. The vascular wall of the human radial artery showed variable positivity with the following applied antibodies: Kv1.2, Kv1.3, Kir6.1, and K Ca1.1. The antibodies against Kv1.6, Kv2.1, and Kir6.2 channel subunits were completely negative. These results suggest that the inhibitory effect of pinacidil on contractions of the human radial artery might be postsynaptic and associated with opening of smooth muscle Kir6.1-containing K ATP channels. TEA- and 4-AP-sensitive K + channels may also contribute to pinacidil effect in the human radial artery.

Inhibition of hypoxic coronary vasoconstriction by pinacidil

Acute hypoxia causes constriction of isolated coronary arteries from several species. The present study was designed to test whether pinacidil, a potassium channel opener, inhibits hypoxiainduced contraction of porcine isolated coronary arteries. Coronary arterial rings were suspended in organ baths for isometric tension recording. Hypoxic contractions were evoked by rapidly changing the gas mixture from 95% O 2/5% CO 2 to 95% N 2/5% CO 2 in preparations partially contracted with KC1. Pretreatment with pinacidil (10 −6 to 10 −4 M) caused concentration-dependent inhibition of the contractile response to hypoxia. The inhibitory effect of pinacidil was attenuated by the k atp channel blocker, glibenclamide (10 −6 M). In rings contracted with acetylcholine, glibenclamide caused a rightward shift in the concentration-response curve to pinacidil while having no effect on the vasorelaxant responses to sodium nitroprusside and diltiazem, thus confirming the specificity of glibenclamide for potassium channel opener-mediated responses. Taken together, the data indicate that pinacidil prevents hypoxia-induced contraction of porcine coronary arteries, and that the effect of pinacidil may be mediated by the opening of glibenclamide-sensitive potassium channels.

A comparison of the relaxant effects of pinacidil in rabbit renal and mesenteric artery

1. 1. The relaxant effects of pinacidil were compared in isolated rabbit renal and mesenteric artery. 2. 2. Pinacidil (10 nm–300 μM) relaxed renal and mesenteric arterial rings precontracted with phenylephrine with p D 2 values of 5.11 ± 0.03 and 6.27 ± 0.04, respectively. 3. 3. The inhibitory effect of pinacidil on the rabbit mesenteric artery was competitively antagonized by glibenclamide (1–10 μM). The calculated p K B value was 6.37 ± 0.04. On the renal artery, glibenclamide (2–20 μM) did not significantly affect pinacidil-induced relaxation ( P > 0.05). 4. 4. Tetraethylammonium (TEA, 1–10 mM) competitively antagonized the pinacaidil induced relaxation of the rabbit renal artery. The p K B value was 3.22 ± 0.08. On the mesenteric artery TEA antagonized the effect of pinacidil in a noncompetitive manner. 5. 5. The concentration-response curves for pinacidil on the rabbit renal and mesenteric artery were not affected by apamin (0.1 μM). 6. 6. It is concluded that ATP-sensitivie K + channels (K ATP) are not involved in pinacidil action on the rabbit renal artery. On the contrary, K ATP are probably major sites of pinacidil action on the rabbit mesenteric artery.

Effects of pinacidil on cerebral and mesenteric arteries--influence of the endothelium.

The effect of pinacidil on the contractile response to stepwise increases of the extracellular K+ concentration ([K+]o) was investigated in isolated segments of human pial and mesenteric arteries and rabbit basilar and mesenteric arteries. The [K+]o eliciting half maximum contraction (EC50) was lower in human pial (18 mM) and rabbit basilar (27 mM) arteries than in human (33 mM) and rabbit (32 mM) mesenteric arteries, respectively. The alpha-adrenoceptor blocker, prazosin, increased the EC50 value for K+ from 27 to 40 mM and reduced the maximum response in rabbit mesenteric arteries, but had no effect on the K(+)-induced contraction in rabbit basilar arteries, indicating a substantial noradrenergic component of the K+ response in the former arteries. Removal of the endothelium decreased the EC50 value for K+ from 27 to 15 mM in rabbit basilar arteries, whereas the K+ sensitivity was unaffected in rabbit mesenteric arteries. Pinacidil shifted the K+ concentration-response curve to the right in human and rabbit cerebral and mesenteric arteries. In rabbit basilar arteries, but not in mesenteric arteries, the shift was larger in the absence than in the presence of an intact endothelium. When endothelium-denuded rabbit arteries were compared, the inhibitory effect of pinacidil was larger in basilar than in mesenteric arteries. Thus, pinacidil inhibits K(+)-induced contractions in both cerebral and mesenteric arteries, but appears to act preferentially on endothelium-denuded rabbit basilar arteries. Provided that endothelial damage and depolarization-induced vasoconstriction are of pathophysiological importance in cerebrovascular disorders such as stroke and cerebral ischemia secondary to vasospasm after subarachnoid hemorrhage, pinacidil may have a therapeutic potential.

Inhibition by the putative potassium channel opener pinacidil of the electrically-evoked release of endogenous dopamine and noradrenaline in the rat vas deferens

The effect of pinacidil on the release of endogenous noradrenaline and dopamine from the sympathetic innervation of the rat vas deferens was examined. Amine release was evoked by electrical stimulation (1, 2, 5 and 10 Hz) or by depolarization with high potassium (75 mmol/l) in the medium. Dopamine and noradrenaline were measured by means of high pressure liquid chromatography with electrochemical detection. Pinacidil (1, 5, 10 and 50 mumol/l) produced a concentration-dependent inhibition of the electrically stimulated (2 Hz) overflow of noradrenaline and dopamine. Only pinacidil 50 mumol/l increased the spontaneous loss of dopamine and noradrenaline. The inhibitory effects of pinacidil (5 mumol/l) on amine overflow were also observed at other frequencies of stimulation (1, 5 and 10 Hz). The magnitude of the inhibitory effect on noradrenaline release was approximately the same at all frequencies (63% to 56% reduction); for dopamine, the higher the frequency of stimulation, the greater the inhibitory effect of pinacidil (up to 73% reduction). When the preparations were continuously stimulated for 70 min at 2 Hz, pinacidil (5 mumol/l) reduced the overflow of dopamine and noradrenaline during the first 40 or 30 min of stimulation only. The addition of phentolamine (1 mumol/l) to the perifusion medium slightly reduced the inhibitory effect of pinacidil on amine overflow, but the inhibition by pinacidil remained statistically significant. Tetraethylammonium (10 mmol/l) completely abolished the inhibitory effect of pinacidil (10 mumol/l). Pinacidil (5 mumol/l) did not reduce the potassium-evoked release of the amines. The results demonstrate that pinacidil impairs transmitter release from the sympathetic innervation of the rat vas deferens, probably as a consequence of the opening of potassium channels.

The Mode of Action of Pinacidil and Its Analogs P1060 and P1368

In rat portal vein and aorta, pinacidil (0.3-100 microM) inhibited spontaneous mechanical activity (portal vein) and responses to norepinephrine (0.001-100 microM) and to KCl (5-80 mM). Pinacidil and its analogs P1060 and P1368 inhibited established contractions to 20 mM KCl but had little effect on responses to 80 mM KCl. The order of spasmolytic potency was P1060 greater than pinacdil greater than P1368. Intracellular electrical recording showed that in a portal vein, pinacidil (0.3-10 microM) abolished spontaneous electrical activity and hyperpolarised the cells to the region of the calculated EK. Pinacidil (3-10 microM) produced a similar hyperpolarisation in rat aorta, and in both tissues the hyperpolarisation was maintained in the continuing presence of pinacidil. Using 86Rb as a K+ marker, pinacidil increased 86Rb exchange in both the rat portal vein and aorta. The analog P1060 also increased 86Rb efflux in the rat portal vein; P1368 had no significant effect. It is concluded that the inhibitory effects of pinacidil in rat blood vessels are associated with the opening of 86Rb-permeable K+ channels. This mechanism produces a low-resistance pathway in the membrane and this inhibits the ability of pressor agents to produce smooth muscle contraction.