Action Of Pinacidil Research Articles

Glibenclamde blocks the relaxant action of pinacidil and cromakalim in airway smooth muscle

Concentration-relaxation curves for pinacidil and cromakalim were obtained in isolated guinea-pig tracheas contracted by histamine. Pinacidil produced complete relaxation with an EC 50 value of 2.8 μM. The antidiabetic concentration-relaxation curve for pinacidil without changing the maximal relaxant response. Cromakalim produced 85% relaxation with an EC 50 value of 1.1 μM. Glibenclamide (0.1 μM) displaced the concentration-relaxation curve to the right and at higher concentrations (1–10 μM) caused nearly complete suppression of the maximal relaxant response to cromakalim. Glibenclamide not only prevented the effects of pinacidil and cromakalim but also produced a concentration-dependent and complete reversal of submaximal relaxations produced by these drugs. Glibenclamide was a selective antagonist of the relaxation of airway smooth muscle induced by pinacidil and cromakalim. Concentration-relaxation curves for theophylline, terbutaline and verapamil were unaffected by glibenclamide.

Evidence that pinacidil may promote the opening of ATP‐sensitive K+ channels yet inhibit the opening of Ca2+‐activated K+ channels in K+ ‐contracted canine mesenteric artery

1. The effects of cromakalim and pinacidil on contraction and 86Rb efflux were investigated in strips of canine mesenteric artery. 2. Cromakalim and pinacidil relaxed arterial strips precontracted with 20.9 mM K+ with pD2 values of 6.56 and 5.88, respectively. 3. High (above 10 microM) concentrations of pinacidil, but not cromakalim, relaxed arterial strips bathed by a medium containing 65.9 mM K+, and inhibited Ca2(+)-induced contractions in strips bathed by a medium containing 80 mM K+. These findings suggested that pinacidil may act as an inhibitor of Ca2+ influx. 4. In arterial strips preloaded with 86Rb, cromakalim and pinacidil increased the basal 86Rb efflux. 5. When the effects of cromakalim and pinacidil on 86Rb efflux were determined in arterial strips contracted with 65.9 mM K+, both drugs increased 86Rb efflux. The increase in 86Rb efflux induced by pinacidil was much smaller than that induced by cromakalim. Under the same conditions, nifedipine decreased 86Rb efflux. 6. After the addition of nifedipine to arterial strips contracted with 65.9 mM K+, pinacidil produced a greater increase in 86Rb efflux than in the absence of nifedipine, whereas the effects of cromakalim were the same for the two conditions. Therefore, the effects of pinacidil on 86Rb efflux may be the resultant of two opposing effects: an increased 86Rb efflux due to the opening of ATP-sensitive K+ channels, and a decreased efflux due to the closing of Ca2(+)-activated K+ channels. 7. In causing relaxation, cromakalim was competitively antagonized by glibenclamide with a pA2 value of 7.16. However, glibenclamide antagonism of pinacidil was not of the simple competitive type, suggesting that inhibition of Ca2 + influx may contribute to the relaxant action of pinacidil. 8. It may be concluded that although the ability of pinacidil to increase 86Rb efflux via ATP-sensitive K+ channel opening was similar to that of cromakalim, the inhibition of Ca2 + influx by pinacidil may reduce the opening of Ca2 +-activated K+ channels in K+-contracted arterial strips.

Effects of pinacidil, RP 49356 and nicorandil on ATP‐sensitive potassium channels in insulin‐secreting cells

1. The whole-cell patch-clamp technique has been used to investigate the effects of pinacidil, RP 49356 and nicorandil on membrane potential and adenosine 5'-triphosphate (ATP)-sensitive K+ channel currents in the insulin-secreting cell line RINm5F. Interactions between pinacidil, RP 49356, nicorandil, diazoxide and ATP have been studied in excised outside-out membrane patches and open-cells. 2. In RINm5F whole-cells (current-clamp mode) continually exposed to glucose, pinacidil, RP 49356 and nicorandil, at concentrations greater than 100 microM, consistently reversed the effects of the sugar by repolarizing the membrane and terminating voltage-gated Ca2+ spike-potentials. 3. The actions of pinacidil, RP 49356 and nicorandil on membrane potential may be explained by their effects on the opening of ATP-sensitive K+ channels, since all three compounds activated channels in whole-cells (voltage-clamp mode), excised outside-out membrane patches and open-cells, at concentrations greater than 100 microM. Below 100 microM the actions of pinacidil, RP 49356 and nicorandil were weak and inconsistent. 4. The mechanism of channel activation appears to depend on the presence of cytosolic ATP, since in its absence, pinacidil, RP 49356 and nicorandil (greater than 100 microM) had either no effects or inhibited K+ channels. 5. Pinacidil, nicorandil and RP 49356 (200-500 microM) also appeared to open K+ channels inhibited by quasi-physiological concentrations of ATP (4 mM) and ADP (1 mM). However, in comparison to diazoxide their effects were weak. 6. Since pinacidil, RP 49356 and nicorandil have been shown to have effects on smooth muscle preparations at concentrations of 30 microM and below, the data presented in this study may have important implications for any prospective therapeutic application of the drugs, since at the concentrations required to relax smooth muscle cells, hyperglycaemia will be avoided.

Profibrillatory Actions of Pinacidil in a Conscious Canine Model of Sudden Coronary Death

Pinacidil is one of a number of new antihypertensive agents possessing an action that involves an enhanced potassium efflux in cardiac and vascular smooth muscle. An associated feature of pinacidil is a shortening of the cardiac action potential duration, which may constitute a potentially proarrhythmic effect. The present study evaluated pinacidil (0.3 mg/kg/h i.v. for 6 h) on the postinfarcted canine heart in a subset of dogs unresponsive to programmed electrical stimulation during the subacute phase of anterior myocardial infarction, and known to be at low risk of ventricular fibrillation in response to acute posterolateral ischemia. Results were compared with a comparable control group of vehicle-treated, noninducible animals. Nonsustained ventricular tachyarrhythmia developed in 2 of 15 pinacidil-treated animals as compared to the initiation of ventricular tachycardia in 1 of 16 postinfarcted hearts (p = 0.96) in the control group. Thus, pinacidil did not alter the responsiveness of the postinfarcted heart with respect to the electrical induction of tachyarrhythmias. The subsequent development of an acute ischemic event at a site remote from the previous myocardial infarction was associated with a greater incidence of ventricular fibrillation within 1 h from the onset of ischemia in the pinacidil-treated animals (9/15; 60%) as compared to the control group (1/15; 6.7%; p = 0.007). The 24-h cumulative mortality, likewise, was greater in the pinacidil-treated group [13/15 (87%)] as compared to the vehicle-treated control group 3/15; 20%; p = 0.001. Significant cardiovascular and electrophysiologic effects of pinacidil included an increase in heart rate (124 +/- 6-143 +/- 10 beats/min, p less than 0.05) and reductions in the refractory periods of normal (178 +/- 2-166 +/- 4 ms, p less than 0.05) and peri-infarcted (170 +/- 5-185 +/- 5 ms, p less than 0.01) myocardial regions. It is concluded that pinacidil does not alter the responsiveness of the postinfarcted heart to programmed electrical stimulation. However, in the presence of a superimposed acute ischemic event, pinacidil increases the potential for the development of ventricular fibrillation in a subset of postinfarcted animals that otherwise show a low risk with respect to the development of lethal arrhythmias. It is hypothesized that the increased tendency to develop ventricular fibrillation is associated with the pinacidil-induced reduction in the ventricular refractory period. This conclusion is consistent with the known ability of pinacidil to enhance potassium efflux during myocardial repolarization and to decrease the duration of the action potential.

Actions of pinacidil on membrane currents in canine ventricular myocytes and their modulation by intracellular ATP and cAMP

We studied the effects of pinacidil (3-50 microM) on the membrane currents of canine ventricular myocytes, using the whole-cell variant of the patch-clamp technique, and the modulation of these effects by intracellular environment, using the pipette perfusion technique. The following observations were obtained: (1) pinacidil induced a dose-dependent outward shift in current at voltages positive to -70 mV; (2) the pinacidil-induced current was largely time-independent at voltages positive to -50 mV and displayed an increase in current fluctuations at more positive voltages, resembling the kinetic properties of current through the ATP-regulated K+ channels; (3) elevating the extracellular potassium concentration [( K+]o) caused a positive shift in the voltage where the pinacidil-induced current crossed the voltage axis and increased the slope conductance of this current; (4) the pinacidil-induced current was reduced by Ba2+ (0.5-1.5 mM) and abolished by intracellular Cs+ (125 mM); (5) glibenclamide reversibly reduced or abolished the pinacidil-induced current; (6) the action of pinacidil was decreased by elevating [ATP] in the pipette solution (from 1 to 10 mM); (7) the action of pinacidil was augmented by adding isoproterenol (1 microM) to the superfusate or adding cAMP (0.1 mM) to the pipette solution; (8) elevating temperature augmented, and accelerated the onset of pinacidil's action; (9) pinacidil reversibly decreased the Ca2(+)-independent transient outward current (Ito1) but augmented the Ca2(+)-dependent transient outward current (Ito2). Based on these observations, we reached the following conclusions: (1) the main effect of pinacidil is to increase an outward current through the ATP-regulated K+ channels; (2) pinacidil's action is modulated by an enzymatic reaction.

Mechanism of the Vasodilator Action of Pinacidil

The mechanism of the vasodilator action of pinacidil has been studied in rat mesenteric small arteries. The results show, first, that the use of flux studies to make measurements of ion permeability requires knowledge of the membrane potential, especially as regards K+ permeability. Second, the results confirm that the vasodilator effect of pinacidil is due to an increase in K+ permeability. Lastly, the results suggest that the K+ channels involved are sensitive to glibenclamide.

Interaction of potassium channel openers and blockers in canine atrial muscle

1. The possibility that the interaction between potassium channel openers, e.g. cromakalim, pinacidil and nicorandil, and some potassium channel blockers involves a common site was investigated in canine atrial muscle. 2. Cromakalim, pinacidil and nicorandil produced a negative inotropic effect, their pD2 (-log EC50) values being 6.11 +/- 0.07, 5.37 +/- 0.09 and 4.55 +/- 0.07, respectively. 3. The potassium channel blockers, tetraethylammonium (TEA), tetrabutylammonium (TBA), 3,4-diaminopyridine (DAP), CsCl and BaCl2 all produced a positive inotropic effect. 4. The concentration-effect curves for the negative inotropic actions of pinacidil were shifted in a parallel way to the right by low concentrations of TEA, TBA or BaCl2. Maximum responses to pinacidil were depressed by higher concentrations of the blockers. An analysis of the non-competitive antagonism by TEA yielded pKA (-log KA) values of 4.00-4.05 for pinacidil. 5. The concentration-effect curves for cromakalim and nicorandil were shifted by TEA similarly to those for pinacidil, and a similar analysis yielded pKA values of 4.47-4.68 for cromakalim and 3.47-3.74 for nicorandil. 6. The KA values of cromakalim, pinacidil and nicorandil were about 10-30 times greater than their EC50 values, indicating that there are non-linear stimulus-effect relationships between the binding of the three potassium channel openers to their binding sites at potassium channels and their negative inotropic effects. 7. The dissociation constants for TEA could also be estimated from pA2 and pKB values for antagonizing competitively and non-competitively the negative inotropic effects of the three potassium channel openers; they were 3.47-3.89, and did not differ between the potassium channel openers. 8. The concentration-effect curves for the three potassium channel openers were not affected by DAP or CsCl. 9. These results suggest the following: (i) quaternary ammonium compounds like TEA and TBA antagonize the negative inotropic effect of cromakalim, pinacidil and nicorandil by binding to potassium channels, thus preventing binding of the channel openers to the same sites or closely related sites in canine right atrial muscles.

The Action of Pinacidil in the Isolated Human Bladder

The need for effective symptomatic treatment of patients with detrusor hyperactivity is widely recognized. In search of new principles of decreasing bladder contraction we have studied the effects of pinacidil on the isolated human bladder. Pinacidil is a recently developed antihypertensive agent classified as a K+ channel opener, and is believed to depress smooth muscle activity by this action. Pinacidil concentration-dependently depressed contractions elicited by carbachol, low concentrations of K+ (<60mM) and electrical stimulation. In addition it caused a concentration-related increase in the efflux of 86Rb from preloaded detrusor cells. The effects on 86Rb efflux could be inhibited by tetraethylammonium chloride and procaine, but not by apamin, agents known to block K+-channels. The results support the view that part of the pinacidil effect on the human bladder is caused by an opening of K+-channels, efflux of K+ and subsequent hyperpolarization of the detrusor cells. Clinical testing of this new therapeutic principle for treatment of bladder hyperactivity seems justified.

Pinacidil opens K+-selective channels causing hyperpolarization and relaxation of noradrenaline contractions in rat mesenteric resistance vessels.

1. The effects of pinacidil on noradrenaline-induced tone, smooth muscle membrane potential and 42K- and 86Rb-efflux from isolated mesenteric resistance vessels (internal diameter 200 microns) of the rat have been studied. 2. Pinacidil (0.3-10 microM) produced concentration-dependent suppression of noradrenaline-induced tone. 3. Pinacidil (0.3-10 microM) caused concentration-dependent hyperpolarization of the smooth muscle. 4. In rat resistance vessels loaded with 42K, pinacidil (1-10 microM) significantly increased the 42K-efflux rate constant. 5. With the use of 86Rb as a marker for K+, 1 microM pinacidil did not affect the 86Rb-efflux rate constant, while 10 microM pinacidil transiently increased the 86Rb rate constant. 6. The results indicate that the relaxant action of pinacidil in these vessels is due to the opening of K+-channels and consequent hyperpolarization. The K+-channels opened are selective for 42K over 86Rb.

Effects of an antihypertensive vasodilator, pinacidil, on regional blood flow in conscious spontaneously hypertensive rats.

Using a radioactive microsphere method, the effects of hydralazine and a new antihypertensive vasodilator, pinacidil, on systemic and regional hemodynamics were examined and compared in conscious Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). A single intravenous administration of pinacidil decreased mean blood pressure in a dose dependent fashion (0.03-0.3 mg/kg), and the peak effect was observed within a few minutes after administration. The onset of the hypotensive action of hydralazine was relatively slow compared to that of pinacidil, and its peak effect appeared 5-10 min after administration. There was no difference between WKY and SHR in the time course of blood pressure change, but the pressure reduction in WKY was less than that in SHR. We observed regional hemodynamic differences between the normotensive rats and the hypertensive rats. The flow rates in the kidney, spleen, gastrointestinal tract and skin of SHR were significantly lower than those of WKY. The intravenous infusion of pinacidil at a rate of 0.06 mg/kg/min increased cardiac output and heart rate, and selectively increased flow rates in organs with low flow rates compared to normotensive controls except for the spleen. Thus, pinacidil reduced total peripheral resistance of SHR to levels of WKY and normalized hemodynamic abnormalities in SHR. The regional hemodynamic action of pinacidil in SHR was not qualitatively different from that of hydralazine except in a few organs.

In Vitro Studies on the Mode of Action of Pinacidil

(+/-) Pinacidil inhibited noradrenaline-induced contractions in rat aorta and portal vein. The spontaneous tone of guinea-pig bronchial and taenia caeci muscles was relaxed and the spontaneous mechanical activity of rat portal vein was abolished. (+/-) Pinacidil abolished contractions produced by low concentrations of KCl in rat aorta and portal vein, but had relatively little effect on responses to high KCl concentrations. The mechano-inhibitory effects of (+/-) pinacidil were antagonised by tetraethylammonium or procaine. In studies with the purified enantiomers of pinacidil, (-) pinacidil was approximately 20 times more potent that (+) pinacidil. Measurements of electrical activity showed that low concentrations of (+/-) pinacidil selectively inhibited spontaneous electrical discharges in rat portal vein. The duration of multispike electrical complexes was shortened, but spike frequency within a complex and the rate of spike rise and fall were unaffected. At higher concentrations, a dose-dependent hyperpolarisation was observed in both rat aorta and portal vein and the membrane potential approached EK. Using both 86Rb and 42K, (+/-) pinacidil produced a concentration-dependent increase in isotope exchange which correlated with those concentrations at which electrical and mechanical inhibitory effects were observed. Using radioimmunoassay, no pinacidil-induced changes in cyclic AMP or cyclic GMP concentrations were detected in rat aorta. These electrical, ion flux and biochemical measurements suggest that the in vitro mechano-inhibitory effects of pinacidil are associated with the opening of 86Rb-permeable K+ channels in smooth muscle. These effects were observed at concentrations of pinacidil similar to those found in vivo in the plasma of experimental animals and man. It is thus concluded that the hypotensive and antihypertensive effects of pinacidil are the consequence of the cessation of ongoing electrical activity and hyperpolarisation which follows the opening of K+ channels in vascular smooth muscle.

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.

Suppression of Ventricular Arrhythmias After Coronary Artery Ligation by Pinacidil, a Vasodilator Drug

Pinacidil, a new vasodilator compound, has been shown to lower blood pressure in animals and humans by a direct vasodilator effect. We have studied the effects of pinacidil on experimental cardiac arrhythmias in dogs. Pinacidil did not exhibit antiarrhythmic activity on ouabain-induced arrhythmias. In contrast, verapamil had minor antiarrhythmic activity on the ouabain arrhythmia, restoring sinus rhythm in one-third of the dogs studied. Pinacidil suppressed the arrhythmia present 22-24 h after coronary artery ligation at doses which produced a significant reduction in mean arterial pressure. The antiarrhythmic action of pinacidil was not modified by pretreatment with propranolol but appeared to be blunted by the infusion of the alpha-agonist, phenylephrine. Other hypotensive agents, hydralazine and sodium nitroprusside, although producing similar reductions in mean arterial pressure to pinacidil, did not exhibit a consistent antiarrhythmic action in dogs 22-24 h after coronary artery ligation. The calcium antagonist verapamil did not display antiarrhythmic activity on this model. The mechanisms by which pinacidil exerted an antiarrhythmic action have not yet been elucidated. The results of the present study suggest that further studies with pinacidil on myocardial infarct size, myocardial perfusion, and experimental cardiac arrhythmias would be advantageous.