Studies of the K(ATP) channel opening activity of the new dihydropyridine compound 9-(3-cyanophenyl)-3,4,6,7,9,10-hexahydro-1,8-(2H,5H)-acridined ione in bladder detrusor in vitro

The potassium (K+) channel opening activity of ZM244085 (9-(3-cyanophenyl)-3,4,6,7,9,10-hexahydro-1,8-(2H,5H)-acridined ione, CAS 149398-59-4), a novel dihydropyridine (DHP), was ascertained. In a set of functional assays, its mechanoinhibitory effect on myogenic activity of guinea pig bladder detrusor muscles, either mildly or highly depolarized with 15 or 80 mmol/l KCl, was measured. ZM244085 had negligible effect on the tone of the detrusor contracted with 80 mmol/l KCl but reduced the myogenic activity induced with 15 mmol/l KCl (IC50=4.2 +/- 0.4 mumol/l). Glibenclamide, an ATP-sensitive K+ (KATP) channel blocker, competitively antagonized this action of ZM244085 with a pA2 value of 7.6. This functional profile of ZM244085 is similar to that of the prototypic K+ channel opener cromakalim but stands in contrast to that of typical DHP Ca2+ channel blockers such as nifedipine and nimodipine. The membrane potential of the guinea pig detrusor, recorded with intracellular microelectrodes, was hyperpolarized 6.8 +/- 3.1 mV by ZM244085 (10 mumol/l). This hyperpolarization was completely blocked by glibenclamide but not affected by apamin (10 mumol/l), a toxin blocking specifically small conductance and Ca2+ dependent K+ (SKCa) channels. ZM244085 (10 mumol/l) increased the whole cell KATP current in isolated guinea pig detrusor cells by 8.8 +/- 2.5 pA, but failed to activate large conductance and Ca2+ dependent K+ (BKCa) channels in excised inside-out membrane patches from those cells. The results from these studies showed that ZM244085 is a K+ channel opener which activates predominantly KATP channels in vitro to relax bladder detrusors.

Mechanoinhibitory effect of estradiol in guinea pig urinary bladder smooth muscles

The mechanoinhibitory effect of estradiol on the myogenic activity of guinea pig urinary bladder detrusor muscles was studied. In detrusor muscles tonically contracted with 80 mmol/lKCl, 17 beta-estradiol and the nonestrogenic isomer 17 alpha-estradiol at 30 mumol/l reduced the contraction by 64 +/- 3 and 59 +/- 1%, respectively. In detrusor muscles maintained in Ca(2+)-free media and depolarized with 80 mmol/lKCl, the contractile response of muscles to the reintroduction of Ca2+ was inhibited in a dose-dependent manner by 17 beta-estradiol, suggesting that 17 beta-estradiol blocked entry of extracellular Ca2+ into bladder smooth muscle cells and reduced the rise of intracellular Ca2+ required for contraction. In detrusor muscles mildly depolarized with 15 mmol/lKCl, 17 beta-estradiol reduced the myogenic activity with an IC50 of 6.8 +/- 1.3 mumol/l. The higher activity of 17 beta-estradiol in this latter test indicated that estradiol could also possess some K+ channel opening activity. Glibenclamide at 1 mumol/l did not affect the relaxant activity of 17 beta-estradiol in detrusor muscles stimulated with 15 mmol/l; however, this activity was diminished in a dose-dependent manner by iberiotoxin. Collectively, these results have demonstrated that in addition to the Ca2+ antagonist activity, 17 beta-estradiol possesses K+ channel opening activity in guinea pig urinary bladder smooth muscles, activating probably not the adenosine triphosphate sensitive, but the Ca(2+)-dependent large-conductance K+ channels.

Calcium dependent K-channels in guinea pig and human urinary bladder

This study provides evidence for the presence of large conductance Ca(2+)-dependent K-channels in guinea pig and human urinary bladder smooth muscle. A23187, a Ca(2+)-ionophore, increased charybdotoxin and iberiatoxin sensitive 42K efflux in human urinary bladder smooth muscle cells, suggesting that large conductance Ca(2+)-dependent K-channels are present in these cells. NS004, a large conductance Ca(2+)-dependent K-channel opener, relaxed guinea pig bladder strips precontracted with 15 mM KCl which is inhibited by iberiatoxin. In addition, NS004 also evoked an iberiatoxin sensitive increase in 86Rb/42K efflux in guinea pig and human urinary bladder smooth muscle cells, demonstrating that NS004 activates large conductance Ca(2+)-dependent K-channels to achieve its relaxation effect in the bladder.

Zeneca ZD6169 and its analogs from a novel series of anilide tertiary carbinols: in vitro KATP channel opening activity in bladder detrusor

The potassium (K+) channel opening activity of Zeneca ZD6169 and one of its pyridylsulfonyl analogs from the anilide tertiary carbinol series was ascertained. Their mechanoinhibitory effects on the myogenic activity of the guinea pig bladder detrusor muscle were measured in a set of functional assays. Elevating the K+ concentration in the tissue bath from 15 to 80 mmol/l increased the IC50 value of ZD6169 from 1.61 +/- 0.22 223 +/- 37 mumol/l. This result suggests that ZD6169 may act as a K+ channel opener. Similar to the prototypic ATP-sensitive K+ (KATP) channel opener cromakalim, the K+ channel openers from the anilide tertiary carbinol series displayed stereoselective mechanoinhibitory activity only in the test protocol in which the detrusor was stimulated with 15 mmol/l KCl. Being the active enantiomer, ZD6169 has an activity more than 30-fold higher than the less active enantiomer. ZD6169 at 10 mumol/l hyperpolarized the guinea pig detrusor membrane potential by 6.1 +/- 1.2 mV and increased the whole cell KATP current in isolated guinea pig smooth muscle cells by 34.9 +/- 7.9 pA. This is comparable to the increase of 26.8 +/- 5.0 pA obtained with 10 mumol/l of lemakalim, the active enantiomer of cromakalim. The K+ channel opening activity of ZD6169 and the pyridylsulfonyl analog was competitively antagonized by the KATP channel blocker glibenclamide in the guinea pig detrusor with a pA2 value of 7.2. This activity, however, was unaffected by blockers of small and large conductance Ca-dependent K+ channels, such as apamin and charybdotoxin, respectively. The present study showed that Zeneca ZD6169 and its analog from the anilide tertiary carbinol series are K+ channel openers that activate KATP channels in vitro to relax bladder detrusors.

β-Adrenoceptor Subtypes in the Detrusor of Guinea-Pig Urinary Bladder

beta-Adrenoceptors have been demonstrated in the urinary bladders of many animals including the guinea pig. However, there is little information on the subtypes involved in the antispasmodic activity of beta-adrenoceptor activation in the guinea-pig detrusor. The present study uses the non-selective beta-agonist isoproterenol, the antagonist nadolol, the beta 2-selective agonists salbutamol and terbutaline, the antagonist ICI 118551, and the beta 1-selective antagonist metoprolol, to demonstrate functionally the subtypes existing in the guinea-pig detrusor. Isoproterenol dose-dependently reduces the myogenic activity in the guinea-pig detrusor induced by mild depolarization with 20 mM potassium in the tissue bath. At the supramaximal concentration of 30 microM, isoproterenol achieves 73 +/- 2% of the reference maximal response. This activity of isoproterenol is reduced to 9 +/- 5, 24 +/- 6 and 54 +/- 1% in the total blockade of beta, beta 1 and beta 2 with nadolol, metoprolol and ICI 118551, respectively. Consistently, salbutamol and terbutaline at the same concentration produce only 35 +/- 1 and 38 +/- 4% of the response, respectively. Thus, both beta 1- and beta 2-adrenoceptors are present in the detrusor of the guinea-pig urinary bladder. Although activation of either subtype results in antispasmodic action, the larger portion of the antispasmodic activity appears to be associated with the activation of the beta 1-subtype.

Hemodynamic effects of adenosine agonists in the conscious spontaneously hypertensive rat

The present studies examined the underlying hemodynamic mechanisms contributing to the reduction in blood pressure observed in conscious spontaneously hypertensive rats after systemic administration of adenosine agonists. The effects produced by i.v. and i.a. injections of 2-phenylaminoadenosine [CV-1808, adenosine (A2) selective agonist], 5'-N-ethylcarboxamide adenosine (NECA, nonselective agonist), 2-chloroadenosine (2-CADO, A1 selective agonist) and cyclopentyladenosine (CPA, A1 selective agonist) were evaluated and compared to those of hydralazine. All agents produced hypotensive effects after bolus i.v. injection. Although CPA, NECA and 2-CADO elicited dose-dependent bradycardia, CV-1808 and hydralazine increased heart rate. These effects, with the exception of the hydralazine-evoked responses, were attenuated by prior treatment with 8-(p-sulfophenyl)theophylline (2 mg/kg/min), whereas both CV-1808 and hydralazine produced regional vasodilation, significant increases in blood flow occurred only after CV-1808 (3-30 micrograms/kg). The regional hemodynamic responses to NECA were more complex; low doses (0.1-1 microgram/kg) produced consistent reductions in regional vascular resistance, whereas at the highest dose renal vasoconstriction occurred. Although regional vasodilation occurred after 2-CADO, mesenteric vasoconstriction was observed subsequent to CPA administration. Whereas a significant increase in renin release was evident in animals treated with CV-1808 and hydralazine, no change occurred in response to the NECA-, 2-CADO- or CPA-induced hypotension. We conclude that the predominant hemodynamic response after selective activation of A2 receptors is one of regional vasodilation and hypotension leading to a reflex increase in heart rate and renin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation of atrial natriuretic peptide: pharmacologic effects of protease EC 24.11 inhibition

Several processes participate in the clearance of atrial natriuretic peptide (ANP) from the circulation, one of which is enzymatic degradation. Endoprotease EC 3.4.24.11 (NEP 24.11), present within the kidney in high concentration, has been shown in vitro to degrade ANP. Phosphoramidon and thiorphan, two potent NEP 24.11 inhibitors, have been shown to prevent the enzymatic degradation of ANP. The purpose of the present study was to determine if phosphoramidon or thiorphan would alter the in vivo time course of the pharmacologic effects of ANP. The magnitude and duration of the ANP-induced increase in urine output and sodium and cyclic GMP excretion were examined with and without either thiorphan or phosphoramidon. Six separate groups of anesthetized rats received either a low, medium, or high infusion rate of thiorphan or phosphoramidon. Renal responses to ANP were potentiated and prolonged during the low phosphoramidon infusion (3 Ki) and the medium thiorphan infusion (150 Ki). At high inhibitor infusion rates in the anesthetized rat, ANP elicited a marked depressor response. In the conscious spontaneously hypertensive rat (SHR), a 15-min intravenous (i.v.) infusion of ANP (1 microgram/kg/min) lowered mean arterial pressure (MAP 23 +/- 6 mm Hg), with an approximately 35-min duration of action. A simultaneous i.v. infusion of phosphoramidon (high dose) produced both a potentiation (33 +/- 3 mm Hg) and a prolongation (greater than 65 min to return to baseline) of the depressor response. These data lend support to the hypothesis that enzymatic breakdown of ANP may play an important role in regulating the actions of atrial natriuretic peptide.