Effects of diltiazem on electrical and mechanical activities of isolated guinea pig taenia coli

Comparison of the effects of diltiazem and its analogue siratiazem on contractility in arteries, ileum and cardiac muscle

1. The aim of this study was to compare the abilities of diltiazem and siratiazem to inhibit concentration-response curves for contractile responses to calcium in arterial and intestinal smooth muscle and cardiac muscle. 2. Diltiazem and siratiazem inhibited, in a concentration-dependent manner, the maximum contraction produced by cumulative addition of calcium chloride to rabbit mesenteric artery, ileum and paced atria in vitro. The order of potency, as indicated by the IC25 values (with 95% confidence intervals) for siratiazem was ileum, 0.33 microM (0-0.63) > mesenteric artery, 0.75 microM (0.32-1.01) and for diltiazem was ileum 0.1 microM (0.007-0.14) = mesenteric artery 0.13 microM (0-0.22). 3. In rabbit atria, the IC25 was of the order of 10 microM for both siratiazem and diltiazem. 4. Both drugs also inhibited calcium concentration-response curves in sheep cerebral arteries and in this tissue the IC25 values were 1.18 (0.37-1.63) and 0.89 (0-1.36) microM for siratiazem and diltiazem, respectively. 5. It is concluded that siratiazem, like diltiazem, blocks entry of calcium via voltage-operated channels with a similar potency to diltiazem on rabbit ileum and cardiac muscle and sheep cerebral arteries but is less potent on rabbit mesenteric arteries.

Effects of diltiazem on phasic and tonic activity in rat portal vein

The effects of the Ca2+ entry blocking drug, diltiazem, have been evaluated in the rat isolated portal vein, against phasic or tonic responses induced by a range of agonists. Diltiazem was a potent antagonist of phasic responses induced by low concentrations of K+, tetraethylammonium (TEA), the selective alpha 2-adrenoreceptor agonists UK 14304 or TL99 and angiotensin II (AII). Diltiazem was significantly less potent as an antagonist of phasic responses induced by the selective alpha 1-adrenoreceptor agonists phenylephrine (PE) or methoxamine (ME) or the non-selective alpha-adrenoreceptor agonist (NA), or of tonic responses evoked by high concentrations of K+, or PE. The non-stimulated phasic activity of the portal vein was antagonised by diltiazem at higher concentrations only. It is concluded that in the rat portal vein, phasic or tonic activity are associated with different Ca2+-gating mechanisms. It is considered that these differences could represent different Ca2+-channels, different rates of activation or deactivation of the channels, or involve other sources of activator Ca2+ than extracellular Ca2+. The alpha 2-adrenoreceptor subtype may be functionally linked with a voltage dependent Ca2+-channel to cause phasic responses in this preparation.

Diltiazem-induced vasodilatation of smooth muscle cells of the canine basilar artery

1 The effects of diltiazem on smooth muscle cells of the canine basilar artery were investigated by means of microelectrode, double sucrose gap and isometric tension recording methods. 2 The mean membrane potential of the smooth muscle cells was -49.8 mV and they were electrically quiescent. Diltiazem (over 10(-5) M) depolarized the membrane. After pretreatment with 5 and 10 mM tetraethylammonium (TEA), an outward current pulse (1 and 2 s in duration) produced a spike and this spike was abolished by application of 10(-5) M diltiazem. 3 The spike could also be generated by the excitatory junction potential (e.j.p.) evoked by perivascular nerve stimulation (0.05 ms in pulse duration) in the presence of 5 mM TEA. Diltiazem (greater than 10(-6) M) suppressed both the spike and the e.j.ps, the suppression being more apparent for spike generation. The amplitude of the e.j.ps was reduced by diltiazem in concentrations greater than 10(-6) M. The effects were dose-dependent: when the amplitude of e.j.ps was reduced by application of diltiazem, the resulting mechanical response was also proportionally smaller. 4 The contractions evoked by 128 mM [K]o, 10(-3) M adenosine 5'-triphosphate (ATP) or, NaCl-free solution were abolished in Ca-free solutions containing 2 mM EGTA, but the amplitude of caffeine-induced contraction (10 mM) was only slightly reduced. Diltiazem, in concentrations above 3 X 10(-7) M suppressed the contraction evoked by excess [K]o, ATP or caffeine, but the inhibitory action of diltiazem on the K-induced contraction was greatest. 5 Following pretreatment with 2.5 mM [Ca]o, a contraction was evoked by caffeine in Ca-free solution. The amplitude of the caffeine-induced contraction was increased by simultaneous application of 2.5 mM [Ca]o with 128 mM [K]o and to a lesser extent by simultaneous application of 2.5 mM [Ca]o with 5.9 mM [K]o. The amplitude of the caffeine-induced contraction generated in the presence of 5.9 mM or 128 mM [K]o was suppressed to the same extent by application of diltiazem [10(-5) M) during preincubation in [Ca]o. This result suggests that the Ca stored in cell is replenished by Ca-influx from [Ca]o during the resting and active states of the membrane, and that diltiazem has no effect on the mobilization of Ca stored in the cell. 6 Thus, diltiazem acts on the canine basilar artery suppressing the Ca-influx during the active condition as a Ca-spike suppressor and the voltage-dependent Ca-influx induced by excess [K]o or by chemical depolarization. Diltiazem has no effect on the Ca mobilization from the store site. This agent also suppresses the amplitude of e.j.ps due to inhibition of the release of chemical transmitter from nerve terminals following the suppression of the Ca-influx. Diltiazem appears to act as a vasodilator on the canine basilar artery.

Selective action of diltiazem on cerebral vascular smooth muscle in the rabbit: antagonism of extrinsic but not intrinsic maintained tone

Diltiazem selectively reduces the second equilibrium phase of contraction of several arteries and veins in the rabbit to a number of agonists, including norepinephrine, serotonin, histamine and potassium. Its effect is consistent with blockage of the entry of activator calcium from the extracellular space into the vascular smooth muscle cell. It has a preferential action on responses of the basilar artery in comparison with those of the ear and mesenteric arteries and saphenous vein. Although the spontaneously developing, maintained intrinsic tone of the basilar artery and facial vein are very resistant to diltiazem, the spontaneous rhythmic activity of the portal vein is sensitive to its antagonistic action. Findings reported here are consistent with the possibility that diltiazem preferentially blocks receptor-operated and potential-sensitive slow calcium channels of the cerebral artery compared with other systemic vessels tested but has little effect on the mechanisms responsible for maintained intrinsic tone development.

Development of diltiazem, a calcium antagonist: coronary vasodilating and antihypertensive actions

We found that the coronary vasodilating action resides in novel 1,5-benzothiazepine derivatives. The calcium antagonistic property of diltiazem has been demonstrated in vascular and visceral smooth muscles as well as in cardiac ventricular muscle. Although the vasodilating action of diltiazem was the most potent in coronary and vertebral artery, it also dilates other peripheral arteries including renal artery. Antihypertensive action of diltiazem has been shown in several experimental models, such as SHR, renal hypertensive and DOCA/saline rats. Diuretic effect of diltiazem was observed in SHR. Following chronic administration of diltiazem to SHR, the increment of blood pressure was significantly lowered without changing body fluid. In addition, hypotensive action of diltiazem by i.c.v. was observed only at a very high dose. We assume that the vasodilating action of diltiazem is primarily involved in the mechanism responsible for its antihypertensive action.

Effect of diltiazem on insulin secretion. II. Experiments on perfused rat pancreas, anesthetized dogs and conscious rats

Effect of diltiazem on insulin secretion was investigated in the perfused rat pancreas. Experiments were also carried out in anesthetized dogs and conscious rats with and without glucose loading. In the perfused rat pancreas, diltiazem reduced both glucose- and tolbutamide-induced insulin secretion and these effects of diltiazem were reversed with removal of the compound. Inhibition of the glucose-induced insulin secretion caused by diltiazem was counteracted by increasing the concentration of calcium ion. In experiments on intact animals, diltiazem at vasoactive doses produced no significant influence on the basal level of plasma insulin or glucose-induced insulin secretion. These data taken together with findings in previously reported work suggest that diltiazem reduces insulin secretion from pancreatic B-cells in vitro possibly by the calcium-antagonistic property, while the compound exhibits practically no inhibitory action on the insulin secretion in vivo.

The effects of diltiazem (CRD-401) on the membrane and mechanical properties of vascular smooth muscles of the rabbit

1 The effects of diltiazem on electrical and mechanical properties of vascular smooth muscles of the rabbit were examined by various experimental procedures. 2 In the pulmonary artery, diltiazem (0.1 to 10 microgram/ml) did not modify the membrane potential (-56 mV), length constant of the tissue (1.47 mm) or rectifying properties of the membrane. Diltiazem (0.1 to 10 microgram/ml) did not modify the membrane potential of the mesenteric artery (-62.5 mV). 3 Diltiazem (1 to 10 microgram/ml) suppressed mechanical responses of pulmonary and mesenteric arteries induced either by direct stimulation of the muscle (1.0 s pulse) or by neural activation (0.5 ms pulse, 30 Hz and 10 s total duration). Diltiazem suppressed the contraction induced by nerve stimulation to a greater extent than that induced by direct muscle stimulation. 4 When the depolarization-contraction relationship of the smooth muscle of the pulmonary artery was observed by voltage clamp technique, diltiazem (1 to 10 microgram/ml) raised the critical membrane potential to evoke contraction from 5 mV to 12 mV, and reduced the amplitude of contraction obtained at any given depolarization level. 5 In the pulmonary artery, diltiazem (10 microgram/ml) suppressed K-induced contraction and raised the mechanical threshold, while K-induced depolarization was not suppressed. Diltiazem (1 to 10 microgram/ml) also suppressed noradrenaline-induced contraction, raised the mechanical threshold and suppressed noradrenaline-induced depolarization. 6 The vasodilator actions of diltiazem on the vascular smooth muscle were compared to vasodilator actions observed with other Ca-antagonists.

The mode of action of contractile effects induced by external calcium and its related bivalent cations in the KCl-depolarized rat uterus

The cumulative log dose-response curve (DRC) isometrically produced by CaCl2 on depolarized uteri of rats in Ca2+-free KCl Ringer's solution (pH 7.8) showed a plateau-shaped type, when responses were plotted as a percent of the maximal tension of 50 micrometer acetylcholine, whereas those produced by BaCl2 or SrCl2 were a simple sigmoid type with the maximal response near the height of the plateau induced by Ca2+. The plateau phase of Ca2+ was inhibited competitively by Mg2+ (0.5--50 mM) and non-competitively by Mn2+ (30 micrometer--1 mM), whereas the maximal contraction of Ca2+ was not inhibited by either ion. Dantrolene (0.1 mM) inhibited both the plateau and the maximal contraction of Ca 2+ and retained the plateau-shaped type. EGTA (2mM) potentiated the plateau to the maximal response level and changed the DRC induced by Ca2+ to the simple sigmoid type. From these results, the plateau of DRC induced by Ca2+ seems to be mainly due to actions of external Ca2+ on the calcium binding of internal surface of cell membrane, suggesting that the internal surface is the site of the bivalent cations tested.