Inhibitory effects of procaine on contraction and calcium movement in vascular and intestinal smooth muscles

Procaine penicillin alters swimming behaviour and physiological parameters of Daphnia magna

Procaine penicillin (PP) is a β-lactam antibiotic widely used in human and veterinary medicine. Although PP is detected in surface water, little is known on its effects on aquatic invertebrates. Our aim was to determine the influence of PP on swimming behaviour (track density, swimming speed, turning angle, hopping frequency) and physiological activity (oxygen consumption, heart rate, thoracic limb movement) of a freshwater invertebrate Daphnia magna exposed to PP at concentrations of 11.79 mg/L, 117.9 mg/L and 1179 mg/L for 2 h and 24 h. The results showed no mortality; however, reduction of swimming activity manifested by the decreased track density, swimming speed and turning angle noted in Daphnia exposed to all the concentrations of PP. Increase of oxygen consumption was observed after 2-h exposure; however, decrease of this parameter was found after 24 h. PP also reduced heart rate and thoracic limb movement in a concentration-dependent manner. The results suggest that the antibiotic should not induce mortality; however, it may affect swimming behaviour and physiological parameters of Daphnia magna particularly inhabiting aquaculture facilities with intensive antibiotic treatment. On the basis of the present results, we also suggest higher sensitivity of behavioural and physiological parameters of cladocerans than the commonly used endpoints: mortality or immobilisation and their possible application as a part of early warning systems in monitoring of surface water toxicity.

Procaine Attenuates Pain Behaviors of Neuropathic Pain Model Rats Possibly via Inhibiting JAK2/STAT3

Neuropathic pain (NPP) is the main culprit among chronic pains affecting the normal life of patients. Procaine is a frequently-used local anesthesia with multiple efficacies in various diseases. However, its role in modulating NPP has not been reported yet. This study aims at uncovering the role of procaine in NPP. Rats were pretreated with procaine by intrathecal injection. Then NPP rat model was induced by sciatic nerve chronic compression injury (CCI) and behavior tests were performed to analyze the pain behaviors upon mechanical, thermal and cold stimulations. Spinal expression of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3) was detected by qRT-PCR and western blot. JAK2 was also overexpressed in procaine treated model rats for behavior tests. Results showed that procaine pretreatment improved the pain behaviors of model rats upon mechanical, thermal and cold stimulations, with the best effect occurring on the 15(th) day post model construction (p<0.05). Procaine also inhibited JAK2 and STAT3 expression in both mRNA (p<0.05) and protein levels. Overexpression of JAK2 increased STAT3 level and reversed the improvement effects of procaine in pain behaviors (p<0.01). These findings indicate that procaine is capable of attenuating NPP, suggesting procaine is a potential therapeutic strategy for treating NPP. Its role may be associated with the inhibition on JAK2/STAT3 signaling.

Electrophysiological Mechanisms of Gastrointestinal Arrhythmogenesis: Lessons from the Heart

Disruptions in the orderly activation and recovery of electrical excitation traveling through the heart and the gastrointestinal (GI) tract can lead to arrhythmogenesis. For example, cardiac arrhythmias predispose to thromboembolic events resulting in cerebrovascular accidents and myocardial infarction, and to sudden cardiac death. By contrast, arrhythmias in the GI tract are usually not life-threatening and much less well characterized. However, they have been implicated in the pathogenesis of a number of GI motility disorders, including gastroparesis, dyspepsia, irritable bowel syndrome, mesenteric ischaemia, Hirschsprung disease, slow transit constipation, all of which are associated with significant morbidity. Both cardiac and gastrointestinal arrhythmias can broadly be divided into non-reentrant and reentrant activity. The aim of this paper is to compare and contrast the mechanisms underlying arrhythmogenesis in both systems to provide insight into the pathogenesis of GI motility disorders and potential molecular targets for future therapy.

Endothelium-dependent and -independent vasorelaxation induced by CIJ-3-2F, a novel benzyl-furoquinoline with antiarrhythmic action, in rat aorta

AIMS

This study was designed to examine the mechanism of relaxation induced by CIJ-3-2F, a benzyl-furoquinoline antiarrhythmic agent, in rat thoracic aorta at the tissue and cellular levels.

MAIN METHODS

Isometric tension of rat aortic ring was measured in response to drugs. Ionic channel activities in freshly dissociated aortic vascular smooth muscle cells (VSMCs) were investigated using a whole-cell patch-clamp technique.

KEY FINDINGS

CIJ-3-2F relaxed both phenylephrine (PE) and high KCl (60mM)-induced contractions with respective pEC(50) (-log EC(50)) values of 6.91+/-0.07 and 6.32+/-0.06. Removal of endothelium or pretreatment with nitric oxide (NO)-pathway inhibitors N(omega)-nitro-l-arginine methyl ester (L-NAME), N(G)-monomethyl-l-arginine (L-NMMA), N(5)-(1-iminoethyl)-l-ornithine (L-NIO), hemoglobin, methylene blue or 1H-[1,2,4]oxadiazolo[4,2-alpha]quinoxalin-1-one (ODQ) reduced the relaxant effect of CIJ-3-2F. Relaxation to CIJ-3-2F was also attenuated by K(+) channel blockers tetraethylammonium (TEA) or 4-aminopyridine (4-AP), but not by charybdotoxin plus apamin, iberiotoxin, glibenclamide, or BaCl(2). CIJ-3-2F non-competitively antagonized the contractions induced by PE, Ca(2+), and Bay K8644 in endothelium-denuded rings. In addition, CIJ-3-2F inhibited both the phasic and tonic contractions induced by PE but did not affect the transient contraction induced by caffeine. CIJ-3-2F reduced the Ba(2+) inward current through L-type Ca(2+) channel (IC(50)=4.1microM) and enhanced the voltage-dependent K(+) (K(v)) current in aortic VSMCs.

SIGNIFICANCE

These results suggest that CIJ-3-2F induced both endothelium-dependent and -independent vasorelaxation; the former is likely mediated by the NO/cGMP pathway whereas the latter is probably mediated through inhibition of Ca(2+) influx or inositol 1,4,5-triphosphate (IP(3))-sensitive intracellular Ca(2+) release, or through activation of K(v) channels.

Effect of cardioplegic and organ preservation solutions and their components on coronary endothelium-derived relaxing factors

Cardioplegic (and organ preservation) solutions were initially designed to protect the myocardium (cardiac myocytes) during cardiac operation (and heart transplantation). Because of differences between cardiac myocytes and vascular (endothelial and smooth muscle) cells in structure and function, the solutions may have an adverse effect on coronary vascular cells. However, such effect is often complicated by many other factors such as ischemia-reperfusion injury, temperature, and perfusion pressure or duration. To evaluate the effect of a solution on the coronary endothelial function, a number of points should be taken into consideration. First, the overall effect on endothelium should be identified. Second, the effect of the solution on the individual endothelium-derived relaxing factors (nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor) must be distinguished. Third, the effect of each major component of the solution should be investigated. Lastly, the effect of a variety of new additives in the solution may be studied. Based on available literature these issues are reviewed to provide information for further development of cardioplegic or organ preservation solutions.

Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle

The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.

Effects of local anesthetics on human bladder contractility

AIMS

We investigated the invitro effects of local anesthetics on the contractility of the human bladder.

METHODS

By measuring the invitro isometric contractions of human bladder strips, we determined the effects of tetracaine, bupivacaine, lidocaine, and ropivacaine on the basal spontaneous contractions and contractions induced by various stimuli, namely, KCl (60 mM), carbachol (CCh), and electrical field stimulation (EFS). The effect of local anesthetic agents on Ca(2+)-independent sustained tonic contraction (SuTC) of the detrusor was also investigated.

RESULTS

Local anesthetics increased phasic and tonic spontaneous contractile activity dose dependently in the concentration range 1-500 muM, but abolished phasic activity at higher concentrations. Local anesthetic agents inhibited nerve-mediated contraction (EFS, 0.8 msec) in a concentration-dependent manner (ropivacaine > tetracaine = bupivacaine > lidocaine), and inhibited non-nerve mediated contractions induced by KCl, long pulse EFS (direct muscle stimulation, 100 msec), and CCh. Inhibitory potency on non-nerve mediated contraction was for long pulse EFS: ropivacaine = tetracaine > bupivacaine = lidocaine and for KCl- and CCh-induced contractions: ropivacaine > tetracaine > bupivacaine = lidocaine. Higher concentrations of local anesthetics were needed to inhibit non-nerve-mediated bladder contraction than nerve-mediated contraction. SuTC was suppressed by all local anesthetics concentration dependently.

CONCLUSIONS

Our study demonstrates that local anesthetics have inhibitory effects on the contraction of human bladder as induced by different stimulants and concentrations. Their effects and differences suggest that they may be considered potentially useful as diagnostic and therapeutic agents for bladder dysfunction.

Green tea catechins evoke a phasic contraction in rat aorta via H2O2-mediated multiple-signalling pathways

1. The contractile effects of tea polyphenols (TP) and its four principle catechins, namely (-)-epicatechin (EC), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG), on rat aorta contractility were investigated using the isometric tension recording technique. 2. At concentrations of 5-100 mg/L, TP evoked phasic contraction of rat aorta in a concentration-dependent but endothelium-independent manner. Of the four catechins tested, EGCG and EGC (3-300 micromol/L), but not EC and ECG, mimicked the contractile response to TP, suggesting that the epigallol moiety in the B ring may be associated with the contractile effect. 3. Contractions in response to EGCG and EGC were not affected by several endogenous vasoconstrictor receptor antagonists, but could be abolished by 10 micro mol/L BAPTA-AM, a membrane-permeable Ca2+ chelator, or attenuated by removal of extracellular Ca2+, suggesting the involvement of both intracellular and extracellular Ca2+ in evoking the contraction. 4. Pretreatment with non-selective Ca2+ channel antagonists mefenamic acid (10 micro mol/L), tetrandrine (30 micro mol/L) and SKF 96365 (30 micromol/L), but not nifedipine (1 micromol/L), the selective inhibitor of voltage-dependent Ca2+ channels, inhibited the contractile responses to EGC and EGCG, indicating the involvement of Ca2+ influx via non-voltage dependent Ca2+ channels. 5. Several intracellular Ca2+ channel modulators, including procaine (5 mmol/L), dantrolene (30 micromol/L) and 2-amino ethoxydiphenyl borate (50 micromol/L; an inositol 1,4,5-trisphosphate receptor inhibitor), also inhibited EGCG- and EGC-induced contractions, thus suggesting a role of intracellular Ca2+ release in these contractions. 6. Both EGCG- and EGC-induced contractions were depressed, to different degrees, by inhibitors of several receptor-coupled enzymes, including phospholipase C, protein kinase C, phospholipase A2 and tyrosine kinase. Furthermore, both EGCG- and EGC-induced contractions were completely abolished by catalase, but not by superoxide dismutase or mannitol/dimethyl sulphoxide. 7. Taken together, these data show, for the first time, that TP and its related catechins that contain an epigallol structure in the B ring, as in EGCG and EGC, exert direct contractile effects on rat aortic smooth muscle via a H2O2-mediated pathway.

Procaine in cardioplegia: the effect on EDHF-mediated function in porcine coronary arteries

OBJECTIVES

Hyperkalemia in cardioplegia impairs the endothelium-derived hyperpolarizing factor (EDHF)-mediated function. This study examined the effect of procaine in cardioplegia on the EDHF-mediated response in porcine coronary arteries.

METHODS

An isometric force study was performed in a myograph. Two rings taken from the same artery (diameter 200-450 microm) were incubated with Krebs solution (group I) or 20 mM K+ (group II) with/without procaine (1 mM) at 37 degrees C for 1 hour. The EDHF-mediated relaxation was induced by bradykinin (BK, -10 approximately -6.5 log M) after U46619 (-8 log M, in group I) or K+-precontraction (in group II) in the presence of indomethacin (7 microM), NG-nitro-L-arginine (300 microM), and hemoglobin (20 microM). The membrane potential of a single smooth muscle cell was measured by a microelectrode after superfusion with Krebs solution with/without procaine for 1 hour.

RESULTS

The EDHF-mediated relaxation was increased by the treatment with procaine with the EC50 shifted leftward (97.3 +/- 0.6% vs. 83.0 +/- 5.1% at -7 log M and 99.4 +/- 0.6% vs. 96.7 +/- 1.6% at -6.5 log M, p < 0.05; EC50: -8.57 +/- 0.24 vs. -7.92 +/- 0.23 log M, p < 0.05). Procaine decreased the BK-induced hyperpolarization from -72.3 +/- 0.7 mV to -68.8 +/- 0.8 mV (-6.5 log M, p < 0.01). The EDHF-mediated relaxation in arteries exposed to 20 mM K+ was not altered by procaine (49.9 +/- 7.4% vs. 55.8 +/- 7.6%, p > 0.05).

CONCLUSIONS

In the coronary arteries, procaine has a depolarizing effect but it enhances EDHF-mediated relaxation. Addition of procaine in cardioplegia did not change the EDHF-mediated endothelial function.

EFFECTS OF LOCAL ANESTHETICS ON THE CONTRACTILITY OF RAT BLADDERS

PURPOSE

We investigated the effect of local anesthetic agents on the detrusor muscle in rats.

MATERIALS AND METHODS

In vitro isometric contraction of rat detrusor strips was measured. We investigated the effects of tetracaine, bupivacaine and lidocaine on baseline spontaneous contractions and contractions induced by various stimuli, including 60 mM. KCl, carbachol and electricalal field stimulation with a pulse duration of 0.8 or 100 milliseconds.

RESULTS

Local anesthetic agents have complex effects on baseline spontaneous contractility that depend on the type of agent used and its concentration. These agents inhibited nerve mediated contraction resulting from electricalal field stimulation with a pulse duration of 0.8 milliseconds in a concentration dependent manner and also inhibited nonnerve mediated detrusor contractions induced by KCl, carbachol or electricalal field stimulation with a pulse duration of 100 milliseconds Higher concentrations of local anesthetic agents were needed to inhibit nonnerve than nerve mediated contractions. In rat detrusor muscle carbachol induced a sustained tonic contraction even after the depletion of internal and external Ca2+ sources, which was also inhibited by local anesthetic agents.

CONCLUSIONS

These results show that local anesthetic agents have a wide spectrum of inhibitory effects on the contraction of bladder smooth muscle induced by various stimulants at different concentrations, which may be potentially useful for treating overactive bladder.

Contribution of nitric oxide and K+ channel activation to vasorelaxation of isolated rat aorta induced by procaine

The endothelium-dependent and -independent relaxant effect of procaine was examined in isolated rat aortic rings. Procaine induced relaxation of arteries precontracted with phenylephrine or with 60 mM K+ in a concentration-dependent manner (0.01-3 mM). Procaine (1 mM) inhibited the transient contraction induced by caffeine (10 mM) in Ca2+-free Krebs solution. Removal of the endothelium caused a rightward shift of the concentration-response curve for procaine. N(G)-Nitro-L-arginine (L-NNA, 10-100 microM), N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM) and methylene blue (1-10 microM) significantly attenuated the procaine-induced relaxation without affecting the maximal response. L-Arginine (1 mM) partially but significantly antagonized the effect of L-NAME (100 microM). Pretreatment of endothelium-intact aortic rings with procaine (1 mM) or with acetylcholine (10 microM) significantly elevated the tissue contents of cyclic GMP and this increase was inhibited in the presence of 100 microM L-NNA. Tetrapentylammonium ions (1-3 microM) reduced the procaine-induced relaxation in both endothelium-intact and -denuded arteries. Tetrapentylammonium ions (3 microM) did not affect the procaine-induced relaxation of 60 mM K+-contracted arteries. Tetraethylammonium ions (3 mM) inhibited the procaine-induced relaxation. In contrast, iberiotoxin (100 nM), glibenclamide (3 microM), 4-aminopyridine (3 mM) and indomethacin (10 microM) had no effect. These results indicate that the procaine-induced relaxation may be mediated through multiple mechanisms. A substantial portion of the procaine-induced relaxation in rat aorta was caused by nitric oxide but not by other endothelium-derived factors. The activation of tetrapentylammonium- and tetraethylammonium-sensitive K+ channels contributes in part to the procaine-induced vasorelaxation. Besides, procaine may directly inhibit both external Ca2+ entry and internal Ca2+ release in aortic smooth muscle cells.

Vasorelaxant effects of purified green tea epicatechin derivatives in rat mesenteric artery

The effects of four epicatechin derivatives, (-) epicatechin, (-) epicatechin gallate, (-) epigallocatechin and (-) epigallocatechin gallate, isolated from jasmine green tea, on the contractions were studied in mesenteric arteries isolated from male Sprague-Dawley rats. All four derivatives (30-500 microM) non-competitively reduced the contractile response to phenylephrine in a concentration-dependent manner with epigallocatechin gallate being the most potent. The relaxant effects of epicatechin derivatives were unaffected by the ATP-sensitive K+ channel blocker glibenclamide (3 microM) or the Ca2+-activated K+ channel blocker charybdotoxin (100 nM). Four epicatechin derivatives also reduced the sustained contractions induced by phenylephrine (1 microM) and endothelin I (5 nM) in normal Krebs solution, whilst they did not relax the phorbol 12-myristate 13-acetate (TPA, 2 microM)-contracted arteries in the absence of extracellular Ca2+. In arteries contracted with 60 mM K+, each of epicatechins caused a relaxation. However, epicatechin derivatives did not affect the transient contraction induced by 100 microM caffeine in Ca2+-free solution. The present results suggest that epicatechin derivatives from green tea leaves relaxed rat mesenteric arteries probably by inhibiting Ca2+ influx. The protein kinase C-dependent contractile pathway and intracellular Ca2+ release may not be involved.

Effects of K+ channel inhibitors on the basal tone and KCl- or methacholine-induced contraction of mouse trachea

The present study examined the effects of K+ channel inhibitors on the basal tone and on KCl- or methacholine-induced contraction of the mouse-isolated trachea. Glibenclamide and iberiotoxin, procaine, quinine and tetraethylammonium did not induce any contraction of the indomethacin-treated mouse trachea. 4-Aminopyridine induced concentration-dependent contraction. This action of 4-aminopyridine was abolished by atropine and reduced by tetrodotoxin and nifedipine. Glibenclamide failed to modify KCl- or methacholine-induced contraction. Iberiotoxin and 4-aminopyridine potentiated KCl- and methacholine-induced contractions. Nifedipine, procaine, quinine and tetraethylammonium inhibited KCl- and methacholine-induced contractions. These data suggest that the closure of large Ca2+-dependent K+ channels can potentiate KCI- and methacholine-induced contraction. The effects of 4-aminopyridine on the mouse trachea reflect chiefly activation of muscarinic receptors. Procaine, quinine and tetraethylammonium inhibit depolarization-induced and receptor-mediated contractions of the mouse-isolated trachea.

Studies on vasorelaxation by tetrapentylammonium ions in rat aortic rings

Tetrapentylammonium ions (TPA+) relaxed the isolated rat aortic rings precontracted with phenylephrine and high extracellular K+ in a concentration-dependent manner with respective IC50 values of 38.9 +/- 3.9 microM and 40.2 +/- 2.9 microM. Other quaternary ammonium ions with a carbon side chain of varying length did not induce relaxation. The relaxant effect of TPA+ was independent of the presence of the endothelium, and was unaffected by various putative blockers of K+ channels such as iberiotoxin (100 nM), glibenclamide (3 microM) and 4-aminopyridine (1 mM). In addition, tetrodotoxin (3 microM), indomethacin (10 microM) and methylene blue (10 microM) had no effect on the TPA+-induced relaxation. TPA+ (50 microM) and procaine (10 mM) completely abolished the phasic contractile response to caffeine in Ca2+-free solution. In the absence of extracellular Ca2+, phorbol 12,13-diacetate (PDA) evoked a sustained tension and TPA+ concentration-dependently reduced the contraction with IC50 of 30.7 +/- 3.1 microM. TPA+ reduced the sustained tension of the similar magnitude induced by phenylephrine, 60 mM K+ and active phorbol ester with similar potencies. These results indicate that TPA+ could act as a non-selective relaxant in arterial smooth muscle. This vasorelaxant effect is unique for TPA+ since other quaternary ammonium ions did not show the similar action in the rat aorta.

Interaction of local anaesthetics with histamine H1 receptors in guinea-pig ileum

The interaction of amine local anaesthetics and related compounds with histamine H1 receptors was investigated in guinea-pig ileal longitudinal muscle. Quinacrine, chloroquine, tetracaine and procaine inhibited [3H]mepyramine binding to solubilized membrane from ileal muscle with pKi values of 5.27 +/- 0.11, 5.66 +/- 0.01, 4.28 +/- 0.08 and 3.97 +/- 0.11, respectively. The pKB values obtained from the initial parallel shift of the dose-response curves for histamine in the presence of these drugs were 5.49 +/- 0.11, 6.14 +/- 0.09, 4.86 +/- 0.06 and 4.58 +/- 0.06, respectively, in reasonable agreement with the pKi values. The combined dose-ratio test with both local anaesthetics and antagonist (mepyramine) present showed that tetracaine and procaine were competitive and chloroquine was partially competitive, but that quinacrine was not competitive at histamine H1 receptors. These local anaesthetics inhibited histamine-induced desensitization in guinea-pig ileum. Receptor occupancy (%) by agonist decreased from 95.2 (without inhibitor) to 73.9, 42.8, 35.9 and 33.9 in the presence of quinacrine, chloroquine, tetracaine or procaine, respectively, under the conditions where each inhibitor drug induced half maximum inhibition of desensitization. The results suggested that most of these local anaesthetics interacted competitively at histamine H1 receptors and inhibited desensitization through their antagonizing actions, whereas quinacrine interacted allosterically and inhibited desensitization through a separate action.

Ca(2+)-induced inhibition of 45Ca2+ influx and Ca2+ current in smooth muscle of the rat vas deferens

The present study investigates how changes in intracellular Ca2+ concentration modulate the influx of 45Ca2+ in isolated rat vasa deferentia. Raising extracellular K+ concentration ([K+]0) to > or = 32 mM increased 45Ca2+ influx during the 1st min in solutions containing 0.03-1.5 mM extracellular Ca2+ concentration ([Ca2+]0). During the 6th min in [K+]0 > or = 50 mM, 45Ca2+ influx was less than during the 1st min. This decline in 45Ca2+ influx occurred for [Ca2+]0 > or = 0.4 mM. Procaine potentiated K(+)-stimulated 45Ca2+ influx in 1.5 mM [Ca2+]0 and eliminated the decline of 45Ca2+ influx in low [Ca2-]0. Ryanodine and norepinephrine reduced K(+)-stimulated 45Ca2+ influx. 45Ca2+ content changed with time in accordance with the changes observed in 45Ca2+ influx. In isolated cells, voltage-dependent inward currents inactivated more rapidly with 1.5 mM Ca2+ as the charge carrier than with 1.5 mM Ba2+, and the steady-state inactivation relationship was shifted in the hyperpolarizing direction. Inward current was reduced with either caffeine, ryanodine, or norepinephrine. The inhibitory effects of norepinephrine were abolished by depletion of intracellular Ca2+ stores. These results are compatible with the hypothesis that K(+)-stimulated 45Ca2+ influx declines with time due to Ca(2+)-induced inhibition of Ca2- channels. Ca(2+)- and inositol 1,4,5-trisphosphate-induced releases of Ca2+ from the sarcoplasmic reticulum appear to play an important role in this process.

Modification of Ca2+ metabolism in the rabbit aorta as a mechanism of spasmolytic action of warifteine, a bisbenzylisoquinoline alkaloid isolated from the leaves of Cissampelos sympodialis Eichl. (Menispermaceae)

The regulation of intracellular Ca2+ as a mechanism of spasmolytic activity of a bisbenzylisoquinoline alkaloid, warifteine, isolated from the leaves of Cissampelos sympodialis, Eichl (Menispermaceae) was studied in the rabbit aorta. Warifteine (pD2' 4.12 +/- 0.09) similar to verapamil (pD2' 6.89 +/- 0.05) antagonized, in a noncompetitive and reversible manner, KCl-induced contractions, mediated by Ca2+ entry through voltage-operated channels. Noradrenaline-induced sustained contractions mediated by Ca2+ entry through receptor-operated channels were also inhibited by warifteine (IC50 6.03 x 10(-5) M) and the standard agent sodium nitroprusside (IC50 1.9 x 10(-8) M). In Ca(2+)-free medium, the alkaloid reduced the intracellular Ca(2+)-dependent transient contraction to noradrenaline by inhibiting the release of Ca2+ (IC50 2.6 x 10(-5) M) from the stores and the refilling (IC50 1.9 x 10(-5) M) of the intracellular stores. The standard agent, procaine, also inhibited the release of Ca2+ (IC50 3.2 x 10(-5) M) but had no significant effect on Ca2+ uptake into the stores. Warifteine failed to affect intracellular Ca2+ stores sensitive to caffeine, while procaine inhibited (IC50 7.9 x 10(-4) M) the release of Ca2+ from these stores. The results indicate that warifteine may cause muscle relaxation by inhibiting Ca2+ channels and by modifying the intracellular Ca2+ stores sensitive to noradrenaline.

BaCl2- and 4-aminopyridine-evoked phasic contractions in the rat vas deferens

1. The actions of BaCl2 and 4-aminopyridine, blockers of K+ channels, on the mechanical activity of the epididymal half of the rat vas deferens were investigated. 2. Both BaCl2 and 4-aminopyridine dose-dependently evoked phasic contractions. High extracellular potassium (35-40 mM) caused a tonic contraction but abolished the BaCl2- and 4-aminopyridine-induced phasic activity and reduced the BaCl2-induced sustained component of contraction, but increased the 4-aminopyridine-induced tonic contraction. 3. Omission of calcium from the extracellular medium totally abolished the 4-aminopyridine-induced response but only reduced the mean amplitude of phasic contractions induced by BaCl. 4. Procaine (10 mM), an inhibitor of internal calcium release, completely abolished the phasic activity and reduced the sustained contraction induced by BaCl2. The remaining tone was abolished by nifedipine (1 microM). 5. Tetraethylammonium (1 mM) suppressed the amplitude of the BaCl2-induced phasic contractions, and induced a biphasic increase in tonic tension. 6. The BaCl2-induced responses were resistant to prazosin (1 microM), yohimbine (3 microM), propranolol (3 microM) or atropine (3 microM); in contrast, the 4-aminopyridine-induced activity was effectively inhibited by prazosin (1 microM) attenuated by yohimbine (1 microM) and atropine (1 microM) but not by propranolol (3 microM). The 4-aminopyridine-induced response was abolished by pretreatment of the vas deferens with 6-hydroxydopamine (0.5 mM). 7. The results indicate that the BaCl2-evoked activity in the vas deferens was mainly due to blockade of Ba(2+)-sensitive K+ channels on the smooth muscle plasma membrane. Subsequent calcium entry through the depolarized plasma membrane was needed to trigger generation of phasic contractions. 4-Aminopyridine-induced action, however, was largely mediated by neurotransmitters released from the depolarized nerve terminals as a result of blockade of K+ channels.

[Ca2+]i-sensitive, IP3-independent Ca2+ influx in smooth muscle of rat vas deferens revealed by procaine

1. The actions of procaine (10 mM) on noradrenaline-induced effects on 45Ca-influx, 45Ca-efflux, 45Ca-content, total inositol phosphates, inositol-1,4,5-trisphosphate, and contractile status of the rat was deferens were examined. 2. Noradrenaline alone had no effect on 45Ca-influx or 45Ca-content, but released Ca2+ from intracellular stores as indicated by an increased 45Ca-efflux and increased total inositol phosphates, specifically inositol-1,4,5-trisphosphate, leading to contraction of the rat vas deferens. 3. Noradrenaline, in the presence of 10 mM procaine, increased 45Ca-influx and 45Ca-content. Procaine blocked the noradrenaline-induced 45Ca-efflux, the increase in total inositol phosphates, the increase in inositol-1,4,5-trisphosphate, and contraction. 4. The noradrenaline-induced increase in 45Ca influx which was observed in the presence of procaine was abolished by phentolamine and nifedipine but was not altered significantly by propranolol suggesting that, in the presence of procaine, noradrenaline activates dihydropyridine-sensitive calcium channels through alpha-adrenoceptors. 5. These findings indicate that, in the rat vas deferens, noradrenaline induces contraction by releasing intracellularly stored Ca2+. The effects of procaine appear to be due to its ability to block the release of Ca2+ from intracellular stores. Furthermore, the simultaneous increase in 45Ca influx and inhibition of inositol-1,4,5-trisphosphate formation in tissues treated with procaine plus noradrenaline indicates that Ca2+ influx is independent of inositol-1,4,5-trisphosphate formation.

Extracellular Ca(2+)-dependent potentiation by cocaine of serotonin- and norepinephrine-induced contractions in rat vascular smooth muscle

Using front-surface fluorometry, we determined the effects of cocaine on force and cytosolic Ca2+ concentration ([Ca2+]i) in the rat aorta. We also examined the effects of cocaine on 45Ca2+ influx. Cocaine (10(-7) to 10(-4) M) alone did not alter the resting level of [Ca2+]i and force. Cocaine (< 10(-4) M), in a concentration-dependent manner, potentiated the 10(-6) M serotonin (5-HT)-induced or 10(-8) M norepinephrine (NE)-induced sustained increase in [Ca2+]i and force in the presence of extracellular Ca2+, whereas it had no potentiating effects in Ca(2+)-free solution. Similar potentiating effects of cocaine were observed in pharmacologically denervated strips. Cocaine (10(-5) M) produced a leftward shift of concentration-response curves for both 5-HT- and NE-induced increases in [Ca2+]i and force with no effect on the maximal response or the relations between [Ca2+]i and force. Cocaine (10(-5) M also accelerated the 45Ca2+ influx during activation by 10(-6) M 5-HT or by 10(-8) M NE. Cocaine (> 10(-3) M) inhibited 5-HT-, NE-, and high-K+ depolarization-induced contractions accompanied by decreases in [Ca2+]i in normal physiological salt solution and 5-HT- or NE-induced transient increase in [Ca2+]i and force in Ca(2+)-free physiological salt solution. Thus, low concentrations of cocaine potentiate NE- or 5-HT-induced contraction by augmenting the increase in [Ca2+]i. These potentiating effects may derive from either an increase in the affinity of the receptors to agonists or an increase in the Ca2+ influx. On the other hand, high concentrations of cocaine (> 10(-3) M) have a relaxant effect on vascular smooth muscle, as a result of a decrease in [Ca2+]i.

A patch-clamp study of the Ca2+ mobilization from internal stores in bovine aortic endothelial cells. I. Effects of caffeine on intracellular Ca2+ stores

The effects of agents known to interfere with Ca2+ release processes of endoplasmic reticulum were investigated in bradykinin (BK)-stimulated bovine aortic endothelial cells (BAE cells), via the activation of Ca(2+)-activated potassium channels [K(Ca2+) channels]. In cell-attached patch experiments, the external application of caffeine (1 mM) caused a brief activation of K(Ca2+) channels in Ca(2+)-free and Ca(2+)-containing external solutions. The application of BK (10 nM) during cell stimulation by caffeine (1-20 mM) invariably led to a drastic channel activation which was maintained during a recording period longer than that observed in caffeine-free conditions. In addition, the cell exposure to caffeine (20 mM) during the BK stimulation enhanced systematically the channel activation process. Since a rapid inhibition of BK-evoked channel activity was also produced by removing caffeine from the bath medium, it is proposed that the sustained single-channel response recorded in the concomitant presence of both agents was due to their synergic action on internal stores and/or the external Ca2+ entry pathway resulting in an increased [Ca2+]i. In addition, the local anesthetic, procaine, depressed the initial BK-induced K(Ca2+) channel activity and completely blocked the secondary phase of the channel activation process related to the external Ca2+ influx into stimulated cells. In contrast, this blocking effect of procaine was not observed on the initial caffeine-elicited channel activity and could not suppress the external Ca(2+)-dependent phase of this channel activation process. Our results confirm the existence of at least two pharmacologically distinct types of Ca(2+)-release from internal stores in BAE cells: an inositol 1,4,5-triphosphate (InsP3)-dependent and a caffeine-induced Ca(2+)-release process.

Blockade by the local anaesthetic, tetracaine, of desensitization of Ca-induced Ca release after muscarinic stimulation in smooth muscle

1. Desensitization of contractile responses dependent on release of intracellularly stored Ca elicited by carbachol, histamine or caffeine was measured after desensitizing treatment with carbachol or histamine in the presence or absence of local anaesthetics in Ca-free solution containing 2 mM EGTA in the smooth muscle of guinea-pig taenia caecum. 2. Histamine-induced homologous desensitization was inhibited by tetracaine and procainamide. Dibucaine did not exert an inhibitory effect on the desensitization. This is consistent with our previous findings concerning the effects of local anaesthetics on the desensitization of histamine H1-receptors measured under normal physiological conditions. 3. Carbachol induced a functional change of intracellular Ca stores which resulted in heterologous desensitization. Tetracaine completely blocked carbachol-induced desensitization of the caffeine-elicited contraction, but in the case of carbachol-induced desensitization of carbachol- and histamine-elicited contractions, this blocking effect of tetracaine was very weak and absent, respectively. The other local anaesthetics used did not affect the desensitization. These results suggest that the Ca-induced and inositol trisphosphate-induced Ca release mechanisms were both desensitized by carbachol and that the desensitization of the Ca-induced Ca release mechanism was selectively blocked by tetracaine.

Caffeine-induced contractions in rabbit isolated renal artery are differentially inhibited by calcium antagonists

Caffeine (1-60 mM) induced concentration-dependent, endothelium-independent phasic contractile responses in isolated rabbit renal artery ring preparations. For concentrations of caffeine over 2 mM, responses were mainly the result of intracellular calcium ion mobilization since they were relatively resistant to removal of calcium ions from the bathing medium. The L-type slow calcium channel blocker, nifedipine (10 microM), had no effect and high concentrations of verapamil and diltiazem (10-30 microM) only slight and inconsistent effects (not concentration-dependent) upon these caffeine responses. Likewise, the highly lipophilic calcium antagonists flunarizine and lidoflazine (3-30 microM) only slightly displaced caffeine concentration-response curves to the right and reduced the maximum response. These small inhibitory effects of flunarizine and lidoflazine were not augmented in a calcium-free medium. In contrast, the other lipophilic calcium antagonists, bepridil and fendiline (3-30 microM), produced marked, non-competitive type inhibition of caffeine responses, completely inhibiting responses to the alkaloid at the highest concentration. Furthermore, the inhibitory effects of bepridil and fendiline were markedly augmented in calcium-free medium. These results clearly differentiate bepridil and fendiline from the other calcium antagonists studied. In addition they provide further evidence for effects other than at the cell membrane which could theoretically contribute to the efficacy of bepridil and fendiline as anti-anginal agents.