Calcium ions and relaxation of intestinal smooth muscle induced by papaverine and aspaminol

The effects of Heteromorpha trifoliata on gastrointestinal smooth muscle of the guinea pig

The effects of an aqueous extract of the root bark of H. trifoliata on various smooth muscle preparations were investigated. The extract had no contractile or relaxant effect on guinea pig gastrointestinal smooth muscle (n = 6), trachea (n = 4), taenia coli (n = 6), nor did it affect the spontaneously-beating atrium (n = 5). However, H. trifoliata antagonized ileal contractions induced by acetylcholine, histamine, serotonin (n = 6 for each dose of agonist) and potassium chloride (n = 4) in a concentration-dependent manner. The antagonism was considered to be non-competitive and non-specific in nature. It is concluded that H. trifoliata antagonizes the effects of these various agonists by either preventing calcium influx into the smooth muscle cell, or inhibiting the calcium-induced calcium release mechanism, or preventing the release of calcium from the sarcoplasmic reticulum, or by preventing the binding of calcium to calmodulin. The antagonistic effects exerted by H. trifoliata could explain its rational use in traditional medicine to alleviate abdominal spasms.

Interaction between Bay-K-8644 and various relaxant agents on K+-depolarized contracture of guinea pig taenia coli

1. Interaction between Bay-K-8644 and nifedipine, D600, diltiazem, papaverine or W-7 on a K+-contracture of the guinea pig taenia coli have been investigated. 2. These relaxing drugs except Bay-K-8644 inhibited the K+-contracture in a concentration-dependent manner. 3. Complete inhibition by nifedipine (1 x 10(-7) M) of the contracture was absolutely antagonized by Bay-K-8644 (1 x 10(-6) M), a Ca2+-agonist, an apparent pA2 value of Bay-K-8644 as an antagonist for nifedipine obtained from Schild plot being 7.94 and its slope 0.99. 4. Marked inhibitions by D600 (1 x 10(-5) M), diltiazem (1 x 10(-5) M), papaverine (1 x 10(-4) M) and W-7 (1 x 10(-4) M) were unaffected but mild inhibitions by around IC50 of these relaxing agents, except W-7, were fully antagonized by Bay-K-8644. 5. These results suggest that Bay-K-8644 is a competitive antagonist for nifedipine, but not for other agents, on common Ca2+ channel sites.

Possible mechanisms of a new type of antispasmodic drug, BTM-1042(cis-(--)-2,3-dihydro-3-(4-methyl-piperazinyl)methyl-2-phenyl-1,5-benzothiazepin-4(5H)-one dihydrochloride)

A newly synthesized compound, BTM-1042 (cis-(--)-2,3-dihydro-3-(4-methyl-piperazinyl)methyl-2-phenyl-1,5-benzothiazepin-4(5H)-one dihydrochloride) depressed the twitch responses of the ileum from guinea pig to electrical stimulation at 0.1 Hz. This inhibitory action of BTM-1042 was not influenced by naloxone, a narcotic antagonist. BTM-1042 proved to be almost as active as atropine on electrically stimulated ileum. BTM-1042 also blocked muscarinic receptors but the potency was about 1/3 of that of atropine. The responses of the ileum of guinea pig to nicotine and 5-hydroxytryptamine also were inhibited by BTM-1042. However, BTM-1042 did not influence the release of transmitters from motor, sympathetic, nonadrenergic inhibitory (or purinergic nerve), noncholinergic excitatory nerves and responses of various smooth muscles mediated through drug receptors, except for the acetylcholine receptor. Spontaneous movement of the unanaesthetized rabbit stomach was dose dependently depressed by BTM-1042 (0.04--0.2 mg/kg, i.v.). The potency ratio for BTM-1042 relative to atropine was 7.4. BTM-1042 is apparently a new type of potent, antispasmodic drug.

Inhibitory alpha-adrenergic action of phenylephrine in guinea pig taenia caecum

Phenylephrine, a selective alpha-adrenergic stimulant, caused a maximal relaxation of the taenia from guinea pig caecum in the concentration of 10(-6) g/ml. Phenylephrine in this concentration did not influence intracellular cyclic AMP and cyclic GMP levels. Although phenylephrine abolished the spontaneous spike discharge, no change was detected in 45Ca-uptake and 45Ca-efflux on the tissue level after phenylephrine. Ca-uptake and Ca-release on the subcellular level were also not influenced by phenylephrine. In Ca free-solution phenylephrine inhibited the response to CaCl2. Phenylephrine increased 42K-efflux in the normally polarized taenia and also in the K-depolarized taenia.

Effects of some vasodilators on calcium translocation in intact and fractionated vascular smooth muscle

The "lanthanum method" was used to measure the effects of vasodilators on the 45Ca influx induced in isolated strips of rabbit main pulmonary artery after replacement of NaCl by KCl in the bathing solution. Two Ca antagonists, verapamil and Ro 11-1781, produced dose-dependent inhibitions of 45Ca influx with IC50 values of 3 X 10(-7) and 4 X 10(-6)M, respectively. Papaverine was virtually equipotent with Ro 11-1781 (IC50 = 2 X 10(-6)M). High concentrations of diazoxide (10(-4) to 10(-3)M) and nitroglycerin (10(-3)M) were required to cause inhibitions which did not exceed 40%. While prazosin 3 X 10(-4)M stimulated 45Ca influx, sodium nitrite and sodium nitroprusside had no effect. A comparison of the effects of vasodilators on contraction and 45Ca influx indicated that, of the drugs studied, only Ca antagonists and papaverine may cause relaxation by interfering with Ca influx. While high concentrations (greater than 10(-4)M) of verapamil, papaverine and nitroglycerin produced an inhibition of 45Ca uptake by membrane fractions from rabbit aorta, the other vasodilators tested were inactive.

Relaxation of depolarized guinea pig taenia caecum induced by some antispasmodics

Taenia isolated from the guinea pig caecum were used for the experiments. No inhibitory response of the depolarized taenia to isoprenaline was observed during the significant increase of cyclic AMP level. These observations suggest that the total tissue level of cyclic AMP is not an important determinant of relaxation in the depolarized taenia. Antispasmodics, such as papaverine, benactyzine and Aspaminol (1,1-diphenyl-3-piperidino-butanol hydrochloride) relaxed the depolarized taenia, while the depolarized taenia was not relaxed by concentrations of dibutyryl cyclic AMP sufficient to relax the polarized taenia. Ca uptake by the depolarized taenia was inhibited by papaverine, benactyzine and Aspaminol but not by isoprenaline and dibutyryl cyclic AMP. These results indicate that relaxation of the depolarized taenia induced by the antispasmodics used was mainly due to inhibition of Ca uptake.