Different calcium dependencies of contractile activity of prostatic and epididymal portions of rat vas deferens

• 1.1. The effects of some organic calcium entry blockers and different concentrations of extracellular calcium on electrically-evoked contractions of isolated epididymal and prostatic portions of rat vas deferens were investigated.
• 2.2. Both epididymal and prostatic parts of rat vas deferens responded to single pulse or train electrical field stimulation, with twitch contractions of submaximal amplitude.
• 3.3. Verapamil showed a biphasic action on the contractions produced by single pulse electrical stimulation. In concentrations < 10⁻⁵M, it potentiated the responses of both portions, but at higher concentrations, the excitatory action was overcome by a concentration-dependent inhibitory effect.
• 4.4. Nifedipine reduced the amplitude of electrically-evoked contractions of both portions in a concentration-dependent manner. The ED₅₀ of nifedipine was 3.6 × 10⁻⁸M and 2.1 × 10⁻⁶M in prostatic and epididymal portions, respectively.
• 5.5. Dantrolene sodium reduced the amplitude of electrically-evoked contractions of both portions in a concentration-dependent manner. The ED₅₀ of dantrolene was 1.55 × 10⁻⁴M and 9.1 × 10⁻⁴M in prostatic and epididymal portions, respectively.
• 6.6. Reduction of Ca²⁺ concentration in medium reduced the amplitude of contractions of both portions significantly. This calcium dependence was more apparent in low frequencies of electrical stimulation.

     

Contractile responses and calcium movements induced by α1-adrenoceptor stimulant,norepinephrine, in rabbit iris dilator muscle

• 1.1. The mechanisms involved in contraction of rabbit iris dilator muscle induced by norepinephrine (NE) were studied.
• 2.2. The concentration-response curve of NE was not influenced by Ca²⁺ blockers in the normal physiological saline solution (PSS) and removal of Ca²⁺ from PSS.
• 3.3. In 0.01 mM EGTA containing Ca²⁺-free PSS, the NE-induced contraction was phasic, which was suppressed by TMB-8, cyclopiazonic acid, ionomycin and A23187 but still partly remained.
• 4.4. In 2 mM EGTA containing Ca²⁺-free PSS, NE increased the intracellular Ca²⁺ ([Ca²⁺]_i) and muscle tension. Ryanodine abolished the increase in [Ca²⁺]_i induced by NE but slightly inhibited the tension.
• 5.5. These results suggest that the NE-induced contraction of rabbit iris dilator in normal PSS is mainly due to the increase in the release of intracellularly sequestered Ca²⁺ and partly due to the Ca²⁺-independent processes.

     

Actions of abscisic acid and the analogue SD217595 on calcium mediated activity of rat vas deferens smooth muscle

• 1.1. K⁺-induced and Ca²⁺-induced contractures of rat prostatic and epididymal vas deferens smooth muscle were used to screen ABA and its analogue SD217595 for Ca²⁺ modulatory activity.
• 2.2. The Ca²⁺ agonist BAY K8644 significantly enhanced Ca²⁺-induced contractures while the Ca²⁺ entry blocker nifedipine strongly inhibited such contractures in both types of vas deferens preparation over the whole Ca²⁺ concentration range employed.
• 3.3. At 10⁻⁷ mol 1⁻¹ ABA had no significant effect on K⁺-induced or Ca²⁺-induced contractures nor did it change the phasic/tonic force ratio in the preparations.
• 4.4. The ABA analogue SD217595 strongly inhibited Ca²⁺-induced contractures over the whole Ca²⁺ concentration range employed in both prostatic and epididymal vas deferens.
• 5.5. It is concluded that ABA is without significant Ca²⁺ modulatory activity in this smooth muscle preparation but the ABA analogue SD217595 possesses strong Ca²⁺ entry blocking ability.

     

Effect of Ca2+ Agonist Bay K 8644 in human placental arteries

• 1.1. Bay K 8644 (0.1 μM) induced weak contractions in human placental artery segments that were increased in the presence of 7.5 mM K⁺. K⁺ and serotonin (5-HT) induced contractions that were enhanced by preincubation of segments with Bay K 8644. These enhancements were reduced by nifedipine (0.1 μM) and diltiazem (1 μM).
• 2.2. Bay K 8644 induced a ⁴⁵Ca²⁺ uptake increase which was potentiated by depolarization with K⁺ (less than 30 mM) and antagonized by nifedipine. K⁺ (15 and 30 mM) and 5-HT (1 μM) induced ⁴⁵Ca²⁺ uptake that was enhanced by Bay K 8644.
• 3.3. These results suggest that Bay K 8644: (1) is unable to activate the quiescent potential-operated Ca²⁺ channels (POCs) of these arteries, and (2) activates receptor (5-HT)-operated Ca²⁺ channels or facilitates Ca²⁺ influx through POCs activated by 5-HT.

     

Sensitivity of cardiac tissues with moderate and advanced hypertrophy to calcium ions

• 1.1. Prolonged existence of hypertension is known to induce a compensatory increase in cardiac weight, later followed by a loss of functional responsiveness to biological stimuli.
• 2.2. It was the aim of the present study to investigate the functional responses of hypertrophied hearts to rising levels of intracellular calcium. The experiments were performed using two different degrees of cardiac hypertrophy, the first as obtained in spontaneously hypertensive rats (SHR) of 18–20 weeks old, the second by using rats, 32–34 weeks old, with a surgically induced stenosis of the thoracic aorta (ASR). The ASR, which showed signs of overt heart failure, may be presented as a model for hypertension-induced end-stage cardiac hypertrophy. Age-matched normotensive Wistar-Kyoto rats (WKY) and sham-operated Wistar rats served as respective controls.
• 3.3. Different methods were employed such as increasing the extracellular Ca²⁺concentration, stimulation of calcium influx by means of the calcium entry promoter Bay K 8644, or altering the sodium-calcium exchange by means of the sodium ionophore monensin.
• 4.4. The inotropic responses induced by increasing the extracellular Ca²⁺concentration or provoked by the calcium entry promoter Bay K 8644 proved more pronounced in hearts taken from SHR of 18 weeks old than in those from normotensive control rats, whereas the response to monensin was found to be the same in both types of hearts. In the hearts of ASR, however, the inotropic responses to Ca²⁺, Bay K 8644 and monensin were strongly impaired.
• 5.5. These data demonstrate that in functional experiments the sensitivity to Ca²⁺, which represents the main pathway in establishing a contraction, is strongly reduced in advanced cardiac hypertrophy.

     

A novel phasic contraction induced by dithiothreitol in frog skeletal muscle

• 1.1. Dithiothreitol (DTT), at 50–100 mM, induced a phasic reversible contraction of frog skeletal muscle.
• 2.2. Exposure of single fibers to nifedipine (20 μM), an L-type Ca²⁺ antagonist, blocked the twitch and tetanus tensions but never affected the DTT-induced contraction.
• 3.3. DTT also produced a phasic contraction in fibers where voltage sensors were inactivated in the presence of high K⁺ concentration (190 mM).
• 4.4. A fiber was mechanically skinned after observation of DTT-induced contraction. The skinned fiber contracted in response to a DTT concentration similar to that required to produce contraction in intact fibers before skinning.
• 5.5. In skinned fibers, DTT, at 100 or 200 mM, inhibited the accumulation of Ca²⁺ by SR, but not Ca²⁺ ATPase activity.
• 6.6. These results suggest that a high concentration of DTT triggers Ca²⁺ efflux from the SR through action on the Ca²⁺ release channel and/or closely associated proteins, such as triadin and FK-506 binding protein.

     

Mechanism of the contractile response to Platelet-Activating Factor (PAF) of the rat stomach fundus. I. PAF-induced contractile response and calcium mobilization

• 1.1. Platelet-activating factor (PAF) caused contraction of the rat stomach fundus in a concentration-dependent manner in the presence of atropine, guanethidine, chlorpheniramine, methysergide, indomethacin, nordihydroguaiaretic acid and tetrodotoxin.
• 2.2. PAF produced phasic contraction followed by tonic contraction. The PAF-induced tonic contraction was significantly reduced by treatment with CV-6209, an antagonist of PAF, but phasic contraction induced by PAF was rather resistant to CV-6209.
• 3.3. The contraction induced by PAF was markedly reduced when tissues were previously exposed to PAF (desensitization).
• 4.4. Nicardipine reduced the PAF-induced phasic contraction but not of the tonic contraction.
• 5.5. PAF-induced contractions were almost abolished in Ca²⁺-free medium.
• 6.6. The Ca²⁺-contraction in Ca²⁺-free solution was significantly augmented by PAF, whereas the Ca²⁺-contraction in Ca²⁺-free, isotonic high K⁺ (60 mM) medium was unaffected by PAF.
• 7.7. These results suggest that PAF-induced contractile response in the rat stomach fundus is due to an influx of Ca²⁺ through voltage-dependent Ca²⁺-channels (VDC) and receptor-operated Ca²⁺-channels (ROC). It is further suggested that PAF may depolarize the stomach fundus and this depolarization may open the VDC, whereas PAF may not act directly on the VDC.

     

Vasorelaxant effect of the analgesic clonixin on rat aorta

• 1.1. A novel vasorelaxant effect of clonixinate of l-lysine (Clx), analgesic and anti-inflammatory, was studied in rat aortic rings.
• 2.2. Clx completely relaxed aortic rings contracted by KCl 70 mM and together with its analog flunixin exhibited lesser potency but equal efficacy than verapamil. In comparison, indomethacin, which is a more potent cyclo-oxygenase inhibitor relaxed only about 40% of the maximal contraction of aortic rings.
• 3.3. Furthermore, Clx antagonized Ca²⁺ dependent aortic contraction and BAY K-8644 induced aortic contraction suggesting its calcium antagonist character.
• 4.4. From these results it can be concluded that the hypotensive effect seen in rats in vivo after Clx i.v. injection arises because of vasodilatory effect of Clx and gives further support to the proposal that the pharmacological mechanism of action of Clx should be calcium antagonism.

     

Muscarinic receptor subtypes in the bisected vas deferens of the rat

• 1.1. The nature of muscarinic receptor subtypes in the isolated prostatic and epididymal segments of the vas deferens of the rat were studied.
• 2.2. Presynaptic receptors were characterized in segments under neurogenic transmural stimulation; postsynaptic receptors in segments without stimulation.
• 3.3. The present work suggests that the potency of ACh required to activate muscarinic receptors is higher in the prostatic than in the epididymal segment.
• 4.4. McN-A-343 was only able to induce dose-dependent contractions in the prostatic segment.
• 5.5. The pA₂ value for 4-DAMP suggests that in the prostatic segment the postsynaptical ACh receptors seem to be pharmacologically similar to the ACh-M₃ subtype.
• 6.6. Antagonism of the presynaptic ACh receptor subtype by pirenzepine supports the evidence that these receptors belong to the ACh-M₁ subtype.

     

Effects of tyrosine kinase inhibitor,genistein, and phosphotyrosine—phosphatase inhibitor,orthovanadate, on Ca2+-free contraction of uterine smooth muscle of the rat

• 1.1. The effects of a protein-tyrosine kinase inhibitor, genistein, and a protein-tyrosine phosphatase inhibitor, orthovanadate, were tested on the Ca²⁺-free contraction of the estrogen-dominated rat, which has been proved to be induced mainly via protein kinase C entirely independently of Ca²⁺.
• 2.2. Genistein (30 μM) significantly inhibited the contraction indicating participation of tyrosine kinase activity in the contraction.
• 3.3. Orthovanadate caused contraction concentration-dependently and augmented the Ca²⁺-free contraction at concentrations of more than 1 μM. The contraction by orthovanadate was not inhibited so significantly by genistein (30 μM).
• 4.4. Possible participation of tyrosine kinase activity in Ca²⁺-free contraction is discussed in addition to the formerly reported participation of protein kinase C.

     

Effects of SC-52458, a new nonpeptide angiotensin II receptor antagonist,on increase in cytoplasmic Ca2+ concentrations and contraction induced by angiotensin II and K+-depolarization in guinea-pig taenia coli

• 1.1. The effects of angiotensin (Ang) II receptor antagonist, SC-52458, on peak and plateau components of Ang II-induced contraction were evaluated in the guinea-pig taenia coli.
• 2.2. SC-52458 suppressed both the components of and increases in cytoplasmic Ca²⁺ concentrations, [Ca²⁺]_i, coupled with the contraction by Ang II; tetrodotoxin and atropine did not affect the contractions.
• 3.3. SC-52458 inhibited a plateau component of the contraction induced by K⁺-depolarization to some extent, without affecting a peak component.
• 4.4. SC-52458 suppressed both the contraction and increase of [Ca²⁺]_i by antagonizing AT₁ receptors in the smooth muscle.

     

The effect of Mn2+, Zn2+, Ba2+ and Ca2+ on spontaneous motility in sheep duodenum in vitro

• 1.1. The effects of several ions, Mn²⁺, Zn²⁺, Ba²⁺ and Ca²⁺, on spontaneous motility were investigated in longitudinal smooth muscle strips from sheep duodenum, in vitro
• 2.2. Mn²⁺ (0.5–1.5 mM) and Zn²⁺ (0.5–5 mM) inhibited both the amplitude and frequency of motility in Krebs solution and in Ca²⁺-free medium.
• 3.3. Ba²⁺(0.5–5 mM) evoked three types of contractile responses: (i) an increase in the frequency and a reduction of the amplitude of spontaneous contractions; (ii) a slight increase in muscle tone of the phasic contractions; and (iii) a rapid initial phasic contraction followed by slowly fading contraction. Ca²⁺ induced two kinds of responses in spontaneous motility: (i) a fast phasic contraction, followed by an increase in the amplitude and frequency of phasic contractions with no changes in its tone; and (ii) an increase in the amplitude of contractions.
• 4.4. The Ba²⁺-induced contractions were inhibited by EDTA, verapamil and diltiazem, but were not modified by sodium nitroprusside. The Ca²⁺-induced contractions were reduced by verapamil and diltiazem.
• 5.5. Our results show that Mn²⁺ and Zn²⁺ behave as inhibitors of sheep duodenum motility. In contrast, Ba²⁺ and Ca²⁺ stimulate motility. It is suggested that Ba²⁺ can penetrate the cells through voltage-dependent Ca²⁺ channels and behave as a partial substitute for Ca²⁺.

     

Functional roles of cyclic guanosine 3′,5′-monophosphate analogue in cerebral vasodilation

• 1.1. Vasodilating effects of cyclic nucleotides in cerebral vasculature were examined using membrane permeable cyclic nucleotide analogues, 8-bromoguanosine 3′,5′-cyclic monophosphate (8-Br-cGMP) and 8-bromoadenosine 3′,5′-cyclic monophosphate (8-Br-cAMP).
• 2.2. In isolated canine basilar artery (CBA), 8-Br-cGMP but not 8-Br-cAMP, significantly inhibited Ca²⁺-induced and agonist [serotonin(5-HT), prostaglandin(PG)F_2α or endothelin]-induced contraction, in a concentration-dependent manner.
• 3.3. When Ca²⁺ was depleted from intracellular store sites by pretreatment with A23187, 8-Br-cGMP but not 8-Br-cAMP strongly attenuated contractions induced by Ca²⁺-influx.
• 4.4. Neither 8-Br-cGMP nor 8-Br-cAMP modified contraction induced by caffeine which elicits Ca²⁺ release from intracellular Ca²⁺ store.
• 5.5. 8-Br-cGMP lowered the high K⁺-induced sustained [Ca²⁺] elevation.
• 6.6. These results suggest that, at least in CBA, cGMP exerts its inhibitory effect on the contraction induced by influx of Ca²⁺, by reducing the level of [Ca²⁺]_i and reducing [Ca²⁺]_i sensitivity of the contractile machinery.

     

Effects of nifedipine ryanodine and cyclopiazonic acid on tension development of ileal longitudinal muscle by manganese ions in Ca2+-free high-K+ medium

• 1.1. Mn²⁺ (5 mM) could evoke the contraction in a Ca²⁺-free, high-K⁺ (60 mM) medium in ileal longitudinal muscle. Nifedipine, L-type Ca²⁺ channel blocker, inhibited dose-dependently both the contraction and manganese uptake in the presence of 5 mM Mn²⁺, in the Ca²⁺-free, high-K⁺ medium.
• 2.2. However, both ryanodine, Ca²⁺ release blocker from SR and cyclopiazonic acid, specific SR Ca²⁺-ATPase blocker, had no effects on the contractions evoked by Mn²⁺ and the manganese uptake in the Ca²⁺-free, high-K⁺ medium.
• 3.3. These results suggest that Mn²⁺ did not liberate Ca²⁺ at the storage sites during the Mn²⁺-induced contraction in Ca²⁺-free, high-K⁺ medium. Mn²⁺ is entering via voltage-dependent Ca²⁺ channels in the ileal cell membranes and it directly activates the contractile elements.

     

Are imidazoline receptors involved in sympathetic neurotransmission in rat vas deferens

• 1.1. An involvement of imidazoline receptors in the modulation of neurotransmitter release was investigated in the prostatic portion of the rat vas deferens stimulated transmurally at 0.2 Hz or by single pulses.
• 2.2. Idaxozan and yohimbine induced a concentration-dependent potentiation of the contractile response to 0.2-Hz transmural stimulation in the epididymal and prostatic portion of the vas.
• 3.3. After reserpine treatment, idazoxan, but not yohimbine, still potentiated the contractile response, suggesting a possible involvement of imidazoline receptors.
• 4.4. Clonidine and rilmenidine, agonists with different affinities to α₂-adrenoceptors and imidazoline receptors, inhibited with the same potency the contractile responses to a single pulse transmural stimulation.
• 5.5. Yohimbine (a selective α₂-adrenoceptor antagonist) antagonized the inhibitory concentration effect curve to rilmenidine in a competitive manner. pA₂ values for idaxozan (an antagonist to α₂-adrenoceptors and imidazoline receptors) were not different when noradrenaline or rilmenidine were used as agonists. Phenoxybenzamine blocked the effect of both agonists.
• 6.6. Thus, the potency relationship of agonists, as well as the effect of the antagonists, did not favor the hypothesis that imidazoline receptors are involved in the idazoxan-potentiating effect in the rat vas deferens.

     

Frequency-dependent effects of bay K 8644 on tetanic contractions of frog skeletal muscle

• 1.1. The effects of the calcium channel agonist, Bay K 8644 (1–100 μM), on tetanic contractions, elicited by the stimulation frequencies of 100 Hz, 50 Hz and 25 Hz for 2 s, were investigated on frog skeletal muscle fibers.
• 2.2. Although the area under the tetanic force versus time curve was greatly reduced at the stimulation frequency of 100 Hz, this effect was significantly reversed at the lower stimulation frequencies of 50 and 25 Hz, at all concentrations tested.
• 3.3. During the intracellular recordings, it was revealed that the sodium action potentials elicited with the stimulation frequency of 100 Hz for 2 s were significantly blocked.
• 4.4. Similar to mechanical recordings, the blockade of repetitively elicited action potentials was also significantly reversed at lower stimulation frequencies of 50 and 25 Hz for all concentrations of Bay K 8644 tested
• 5.5. In conclusion, the results indicate that Bay K 8644 depresses both tetanic contractions and action potentials in a frequency-dependent manner in frog skeletal muscle fibers.

     

Effects of organic and inorganic Ca2+-antagonists on acetylcholine-induced contraction in molluscan (Mytilus edulis) smooth muscle

• 1.1. Effect of Ca²⁺-antagonist on the contractile response to acetylcholine (ACh) in molluscan (Mytilus edulis) smooth muscle was investigated.
• 2.2. ACh-induced contraction was remarkably reduced by exposure to Ca²⁺-deprived medium.
• 3.3. The organic Ca²⁺-blockers, verapamil, diltiazem and nicardipine, reduced the concentration-response curve for ACh in a concentration-dependent manner.
• 4.4. The inorganic Ca²⁺-blockers, MnCl₂, NiCl₂, CoCl₂ and CdCl₂, also reduced the concentration-response curve for ACh concentration-dependently.5. ACh significantly increased the amounts of inositol 1,4,5-trisphosphate (IP₃) in the ABRM.
• 5.6. ACh-induced contraction in the ABRM might therefore be mediated through an influx of extracellular Ca²⁺ and Ca²⁺-release from IP₃ sensitive intracellular pools.

     

Multidirectional contraction of human hypertrophied prostate

• 1.1. The purpose of the present investigation is to evaluate muscle contraction in two directions (longitudinal and circumferential to urethra) physiologically and morphologically for α-adrenoceptor agonists.
• 2.2. Norepinephrine (10⁻⁷−10⁻⁴ M), phenylephrine (10⁻⁷−10⁻⁴ M) and clonidine (10⁻⁷−10⁻⁴ M) induced contractions in a dose-dependent manner on human prostate from patients with benign prostatic hypertrophy (BPH).
• 3.3. No significant differences were observed between longitudinal and circumferential directions of human prostate in 50% of the maximal muscle contraction (EC₅₀ values) and the maximal muscle contractions caused by any agents used.
• 4.4. Morphometric analysis for muscle in prostates was performed using formalin-fixed, paraffin-embedded sections stained by the Mallory-Azan method.
• 5.5. There was no significant difference in the density of the muscle area between longitudinal and circumferential directions of prostatic strips.
• 6.6. These results suggest that there are no significant differences in responsiveness of α-adrenoceptor agonists and the smooth muscle contents in longitudinal and circumferential directions to urethra, for human hypertrophied prostate.

     

Effect of trimebutine maleate on the contractile response of the isolated ileum from diabetic rats

• 1.1. Tension of the isolated ileum from diabetic rats induced by streptozotocin was measured isometrically to study the mode of action of trimebutine maleate (TMB).
• 2.2. The hyperreactivity of contractile response to KCl was observed in the isolated ileum from diabetic rats. TMB inhibited the contraction induced by KCl and acetylcholine (ACh) in normal solution.
• 3.3. In Ca²⁺ free solution, the hyperreactivity of contractile response to KCl was attenuated, and TMB did not inhibit the contraction induced by KCl. In contrast, TMB inhibited the contraction induced by ACh even in Ca²⁺ free solution.
• 4.4. These results suggest that the hyperreactivity of contractile response to KCl in the ileum from diabetic rats is due to the enhancement of Ca²⁺ influx through voltage-dependent Ca²⁺ channel and that TMB inhibits the hyperreactivity of contractile response through the inhibition of Ca²⁺ movement by the cell.

     

Actions of manganese ions in contraction of smooth muscle

• 1.1. Manganese ions (Mn²⁺) have been used in the last few decades as one of a number of inorganic Ca²⁺ channel blockers to investigate Ca²⁺ channels in excitable smooth muscle cells.
• 2.2. It has been recently reported that in addition to its inhibitory effects on the Ca²⁺ channels, Mn²⁺ in millimolar concentrations also produces contraction in the state of cell membrane depolarization.
• 3.3. Mn²⁺ has been shown to be able to permeate the cells via voltage-operated L-type Ca²⁺ channels in the membranes and directly activates contractile proteins in smooth muscles.
• 4.4. Intracellular sites of action have been proposed for Mn²⁺ in smooth muscles.