Intracellular Ca2+-calmodulin system involved in the palytoxin-induced K+ release from rabbit erythrocytes.

Palytoxin (PTX) caused K+ release from rabbit erythrocytes which was dependent on the concentrations of extracellular Ca2+ and PTX. In a Ca2+-free solution, PTX still caused a slow K+ release. An intracellular Ca2+ antagonist, TMB-8, an intracellular Ca2+ chelator, quin 2, and calmodulin inhibitors, prenylamine, W-7 and W-5, inhibited the PTX-induced K+ release in a Ca2+-free solution.

Role of endothelium in the contractions induced by norepinephrine and clonidine in rat aorta.

The inhibitory effects of endothelium-derived relaxing factor (EDRF) on the contractions induced by norepinephrine and clonidine in rat aorta were examined. Carbachol induced a relaxation of norepinephrine-induced contraction in rat aorta with endothelium. Removal of endothelium inhibited the carbachol-induced relaxation and increased the magnitude of norepinephrine-induced contraction.

Effects of antimycin A on vascular and intestinal smooth muscle contraction and calcium movements.

The effects of antimycin A on smooth muscle preparations of guinea-pig taenia coli and rabbit aorta were investigated. In guinea-pig taenia coli, antimycin A inhibited the sustained phase but had less effect on the transient phase of K-induced contraction. The inhibitory effect of antimycin A became less in the presence of high concentration (40 mM) of glucose under hypoxia whereas antimycin A strongly inhibited both transient and sustained phase of K-induced contraction in the absence of glucose.

Contractile effects of vanadate on monkey and rabbit tracheal smooth muscle.

The effects of vanadate (Na3VO4: VAN) on isolated tracheal smooth muscle of monkey (Macaca fascicularis) and rabbit were examined. VAN (10(-5)-10(-3) M) induced a sustained contraction in both tracheae which was not affected by atropine, tetrodotoxin or tripelennamine. Indomethacin potentiated VAN-induced contraction in monkey trachea but had no effect in rabbit trachea.

Age-related changes in the sensitivity to verapamil and sodium nitroprusside of vascular smooth muscle of rabbit aorta.

Age-related changes in the sensitivity to verapamil and sodium nitroprusside were examined in isolated aortic strips of the rabbit. In the aortae of newborn rabbits within 10 days of birth, the resting tone of the muscle was strongly reduced by sodium nitroprusside but not by either Ca-deficient solution or by verapamil. High K-induced contraction and noradrenaline-induced contraction were both inhibited by verapamil or sodium nitroprusside.

Increase in membrane permeability in the absence of Ca and Mg in the smooth muscle of guinea-pig taenia coli.

In Ca-deficient smooth muscle of guinea-pig taenia coli, repeated application of high-K solution (45.4 mM) containing Ca induced contractions of similar shape and magnitude. In muscle treated by a Ca- and Mg-deficient solution, however, addition of Ca and K either did not induce contraction or induced only a delayed contraction.

Deficiency of external Ca and Mg increases membrane permeability in the vascular smooth muscle of rabbit aorta.

Effects of a 60 min incubation in Ca- and/or Mg-deficient solutions on the ion contents in vascular smooth muscle of rabbit aorta were examined. In Mg-deficient solution, resting tone of the muscle did not change. Ca-deficient solution increased, whereas Ca- and Mg-deficient solution decreased the resting tone.

Potassium-induced contraction in smooth muscle.

High K-induced contractions in the smooth muscle of rabbit aorta and guinea pig taenia coli may be described as follows: High K depolarizes the smooth muscle cell membrane and opens voltage dependent Ca channels, resulting in an influx of extracellular Ca and an activation of contractile machinery. A part of the cellular Ca is taken up by mitochondria. Oxygen consumption of the muscle increases to compensate for the ATP consumed by contraction.

Calcium channels in smooth muscle.

It appears that, in smooth muscle, there are two distinct types of Ca2+ channel, a voltage-dependent Ca2+ channel and a receptor-linked Ca2+ channel. The former is activated by decreases in membrane potential and the latter is regulated by drug-receptor interactions. These Ca2+ channels exist as separate channels in the aorta of the adult rabbit and of some rat strains; organic Ca2+ antagonists and sodium nitroprusside selectively inhibit each of these two respective channels.

Effects of calcium antagonists on release of [3H]noradrenaline in rabbit aorta.

The effects of several organic Ca antagonists and putative calmodulin antagonists on the release of [3H]noradrenaline from rabbit aorta were examined. A 65.4 mM K solution and electrical stimulation induced a Ca-dependent increase in the 3H-efflux from the adventitial layer (containing nerve terminals) but not from the media-intimal layer.

Effects of vanadate on mechanical and electrical activities in guinea-pig taenia coli.

Effects of vanadate (NH4VO3 and Na3 VO4: VAN) on electrical and mechanical activities and cellular Na content in guinea-pig taenia coli were examined. VAN (1-5 X 10(-4) M) transiently increased membrane potential and decreased muscle tension. Several minutes later, muscle tension increased following membrane depolarization and increase in spike frequency.

Nitroglycerine-induced biphasic relaxation in vascular smooth muscle of rat aorta.

Nitroglycerine induced biphasic relaxation in the rat aorta, previously contracted by noradrenaline; a rapid decrease in tension was followed by a gradual increase reaching a steady level below the control contractile tension. No initial transient relaxation was induced by nitroglycerine in high K-stimulated muscle. The initial transient relaxation, but not the sustained relaxation, was dependent on the concentration of external K; maximum relaxation was observed in the presence of 2.

Comparative effects of verapamil and sodium nitroprusside on contraction and 45Ca uptake in the smooth muscle of rabbit aorta, rat aorta and guinea-pig taenia coli.

The effects of verapamil and sodium nitroprusside on muscle tension and 45Ca uptake activated in different ways were compared in rabbit aorta, rat aorta and guinea-pig taenia coli. In rabbit aorta, K-induced contraction was specifically inhibited by verapamil and noradrenaline-induced contraction by sodium nitroprusside. In rat aorta, both K-induced and noradrenaline-induced contractions were inhibited by verapamil or by sodium nitroprusside also.

The inhibitory effect of X537A on vascular and intestinal smooth muscle contraction.

The effects of X537A (Lasalocid) on contractions induced in vascular and intestinal smooth muscles were examined. High K-induced sustained contractions were inhibited by X537A with an IC50 of 2.8 X 10(-6) M in rabbit aorta and 8.

High K-induced contractions in rabbit and monkey tracheal smooth muscle.

High K-induced contractions in rabbit and monkey tracheal smooth muscle were characterized. A substituted 60 mM K, 94.1 mM Na solution produced a sustained contraction in both preparations.

The inhibitory effects of N2-dansyl-L-arginine-4-t-butylpiperidine amide (TI233) on contraction of vascular and intestinal smooth muscle.

Effects of N2-dansyl-L-arginine-4-t-butylpiperidine amide (TI233) on the contractions in vascular and intestinal smooth muscles were examined. High K-induced sustained contractions in the smooth muscles were inhibited by TI233 with an IC50 of 2.1 X 10(-5) M for rabbit aorta and 3.

Effects of calmodulin antagonists on tension and cellular calcium content in depolarized vascular and intestinal smooth muscles.

1 Several putative calmodulin antagonists have been examined for their inhibitory action on muscle tension and cellular Ca content in the K-depolarized vascular and intestinal smooth muscles. 2 The 65.4 mM K-induced sustained contraction in the media-intimal layer of rabbit aorta and the 45.

Effects of the Na ionophore monensin on the contractile response and the movements of monovalent cations in the vascular smooth muscle of rabbit aorta.

The effects of monensin, a Na ionophore, on the muscle contraction and the movements of monovalent cations were investigated in rabbit aorta. Experiments were conducted in the presence of phentolamine (10(-6) M) to avoid the vasoactive effect of monensin due to the release of endogenous catecholamine. Both monensin (2 X 10(-5) M) and ouabain (2 X 10(-5) M), added separately, produced a small and slowly developing contraction, whereas simultaneous application of these agents produced more rapid and greater contraction.

The inhibitory effect of monensin on high K-induced contraction in guinea-pig taenia coli.

This study deals with the effects of monensin, a Na ionophore, on contraction, cellular Na content, oxygen consumption and tissue ATP content of smooth muscle of the guinea-pig taenia coli depolarized by high K (62.7 mM) solution. The application of monensin (10(-8) -10(-6) M) had little effect on the phasic component of the K contraction while it decreased the tonic component.

High K+,Na+-deficient solution inhibits tension, O2 consumption, and ATP synthesis in smooth muscle.

In guinea pig taenia coli, added 45.4 mM K+ induced a sustained contraction, increased the rate of oxygen consumption, and slightly decreased the ATP content. In substituted 154.

Dissociation of K+-induced tension and cellular Ca2+ retention in vascular and intestinal smooth muscle in normoxia and hypoxia.

In experiments on smooth muscle preparations of rabbit aorta and guinea pig taenia coli, replacement of the external Na+ with K+ produced sustained contraction. When external K+ concentration was increased, cellular Ca2+ retention as measured by a modified lanthanum technique increased. However, when K+ concentration was above 80 mM, the tension decreased despite an increase in Ca2+ retention.

Artificial buffers do not inhibit contractile responses in the smooth muscle of rat portal vein and guinea pig taenia coli.

Effects of substitution for NaHCO3 (and 5% CO2) in the physiological solution with equimolar N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) or morpholinopropane sulfonic acid (MOPS) (and 100% O2) at various pH levels on the contractility of smooth muscle were examined. At pH 7.4, spontaneous contraction in rat portal vein was not inhibited by the artificial buffer solutions, as compared to findings in the case of bicarbonate buffer solution.