Animal models of self-injurious behaviour: an overview.

Self-injurious behaviour is highly prevalent in neurodevelopmental disorders. Interestingly, it is not restricted to any individual diagnostic group. Rather, it is exhibited in various forms across patient groups with distinct genetic defects and classifications of disorders. This suggests that there may be shared neuropathology that confers vulnerability. Convergent evidence from clinical pharmacotherapy, brain imaging studies, postmortem neurochemical analyses, and animal models indicates that dopaminergic insufficiency is a key culprit. This chapter provides an overview of studies in which animal models have been used to investigate the biochemical basis of self-injury, and highlights the convergence in findings between these models and expression of self-injury in humans.

L-type calcium channels and calcium/calmodulin-dependent kinase II differentially mediate behaviors associated with nicotine withdrawal in mice.

Smoking is a widespread health problem. Because the nicotine withdrawal syndrome is a major contributor to continued smoking and relapse, it is important to understand the molecular and behavioral mechanisms of nicotine withdrawal to generate more effective smoking cessation therapies. Studies suggest a role for calcium-dependent mechanisms, such as L-type calcium channels and calcium/calmodulin-dependent protein kinase II (CaMKII), in the effects of nicotine dependence; however, the role of these mechanisms in nicotine-mediated behaviors is unclear. Thus, the goal of this study was to elucidate the role of L-type calcium channels and CaMKII in nicotine withdrawal behaviors. Using both pharmacological and genetic methods, our results show that L-type calcium channels are involved in physical, but not affective, nicotine withdrawal behaviors. Although our data do provide evidence of a role for CaMKII in nicotine withdrawal behaviors, our pharmacological and genetic assessments yielded different results concerning the specific role of the kinase. Pharmacological data suggest that CaMKII is involved in somatic signs and affective nicotine withdrawal, and activity level is decreased after nicotine withdrawal, whereas the genetic assessments yielded results suggesting that CaMKII is involved only in the anxiety-related response, yet the kinase activity may be increased after nicotine withdrawal; thus, future studies are necessary to clarify the precise behavioral specifics of the relevance of CaMKII in nicotine withdrawal behaviors. Overall, our data show that L-type calcium channels and CaMKII are relevant in nicotine withdrawal and differentially mediate nicotine withdrawal behaviors.

The critical role of voltage-dependent calcium channel in axonal repair following mechanical trauma.

Membrane disruption following mechanical injury likely plays a critical role in the pathology of spinal cord trauma. It is known that intracellular calcium is a key factor that is essential to membrane resealing. However, the differential role of calcium influx through the injury site and through voltage dependent calcium channels (VDCC) has not been examined in detail. Using a well-established ex vivo guinea-pig spinal cord white matter preparation, we have found that axonal membrane resealing was significantly inhibited following transection or compression in the presence of cadmium, a non-specific calcium channel blocker, or nimodipine, a specific L-type calcium channel blocker. Membrane resealing was assessed by the changes of membrane potential and compound action potential (CAP), and exclusion of horseradish peroxidase 60 min following trauma. Furthermore, 1 microM BayK 8644, a VDCC agonist, significantly enhanced membrane resealing. Interestingly, this effect was completely abolished when the concentration of BayK 8644 was increased to 30 microM. These data suggest that VDCC play a critical role in membrane resealing. Further, there is likely an appropriate range of calcium influx through VDCC which ensures effective axonal membrane resealing. Since elevated intracellular calcium has also been linked to axonal deterioration, blockage of VDCC is proposed to be a clinical treatment for various injuries. The knowledge gained in this study will likely help us better understand the role of calcium in various CNS trauma, which is critical for designing new approaches or perhaps optimizing the effectiveness of existing methods in the treatment of CNS trauma.

Cotinine inhibits catecholamine release evoked by cholinergic stimulation from the rat adrenal medulla.

The aim of the present study was to clarify whether cotinine affects the release of catecholamines (CA) from the isolated perfused rat adrenal gland, and to establish the mechanism of its action, in comparison with the response of nicotine. Cotinine (0.3-3 mM), when perfused into an adrenal vein for 60 min, inhibited CA secretory responses evoked by ACh (5.32 mM), DMPP (a selective neuronal nicotinic agonist, 100 microM for 2 min) and McN-A-343 (a selective muscarinic M1-agonist, 100 microM for 2 min) in dose- and time-dependent manners. However, cotinine did not affect CA secretion by high K+ (56 mM). Cotinine itself also failed to affect basal CA output. Furthermore, in the presence of cotinine (1 mM), CA secretory responses evoked by Bay-K-8644 (an activator of L-type Ca2+ channels, 10 microM) and cyclopiazonic acid (an inhibitor of cytoplasmic Ca2+-ATPase, 10 microM) were relative time-dependently attenuated. However, nicotine (30 microM), given into the adrenal gland for 60 min, initially rather enhanced CA secretory responses evoked by ACh and high K+, followed by the inhibition later, while it time-dependently depressed the CA release evoked by McN-A-343 and DMPP. Taken together, these results suggest that cotinine inhibits greatly CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does fail to affect that by the direct membrane-depolarization. It seems that this inhibitory effect of cotinine may be exerted by the cholinergic blockade, which is associated with blocking both the calcium influx into the rat adrenal medullary chromaffin cells and Ca2+ release from the cytoplasmic calcium store. It also seems that there is a big difference in the mode of action between cotinine and nicotine in the rat adrenomedullary CA secretion.

New treatment methods in verapamil poisoning: experimental studies.

The aim of this study was to evaluate the effectiveness of the treatment with 4-aminopyridine (4-AP, potassium channel inhibitor) and Bay K 8644 (calcium channel activator) in experimentally evoked verapamil poisoning in rats and to compare the results of this treatment with the effectiveness of widely accepted methods (adrenaline, calcium compounds). The experiment was carried out on male and female Wistar rats which were divided into 4 experimental (A, B, C, D) and a control (K) groups. Rats were anesthetized and the abdominal aorta was cannulated for mean arterial pressure and heart rate measurements while caudal vein was cannulated for drug administration. All animals were infused with verapamil (150 mg/kg/h) until 50% reduction of mean arterial pressure and/or heart rate was observed. After verapamil, control animals were given 0.9% NaCl solution and the other groups received 687.5 mg/kg/h of calcium glucolactobionicum (group A), 0.3 mg/kg/h of adrenaline (group B), 2 mg/kg/h of 4-AP (group C) or 2 mg/kg/h of Bay K 8644 (group D). The mean blood pressure and heart rate was checked and ECG was recorded every 10 min. A statistically significant decrease in mortality compared with the control group was observed in animals treated with adrenaline (p < or = 0.05), Bay K 8644 (p < or = 0.01) and 4-AP (p < or = 0.005). The treatment of experimentally evoked poisoning in rats using 4-AP or Bay K 8644 resulted in fast receding of poisoning symptoms: increase in blood pressure and heart rate, receding of bradyarrhythmia and return of sinus rhythm. The results of the study suggest the usefulness of 4-AP and Bay K 8644 in the treatment of verapamil poisoning.

Niguldipine impairs the protective activity of carbamazepine and phenobarbital in amygdala-kindled seizures in rats.

There is evidence that some calcium (Ca(2+)) channel inhibitors enhance the protective activity of antiepileptic drugs. Since clinical trials have not provided consistent data on this issue, the objective of this study was to evaluate the interaction of a dihydropyridine, niguldipine, with conventional antiepileptics in amygdala-kindled rats. Niguldipine (at 7.5 but not at 5 mg/kg) displayed a significant anticonvulsant effect, as regards seizure and afterdischarge durations in amygdala-kindled convulsions in rats, a model of complex partial seizures. No protective effect was observed when niguldipine (5 mg/kg) was combined with antiepileptics at subeffective doses, i.e. valproate (75 mg/kg), diphenylhydantoin (40 mg/kg), or clonazepam (0.003 mg/kg). Unexpectedly, the combined treatment of niguldipine (5 mg/kg) with carbamazepine (20 mg/kg) or phenobarbital (20 mg/kg) resulted in a proconvulsive action. BAY k-8644 (an L-type Ca(2+) channel activator) did not modify the protective activity of niguldipine (7.5 mg/kg) or the opposite action of this dihydropyridine (5 mg/kg) in combinations with carbamazepine or phenobarbital. A pharmacokinetic interaction is not probable since niguldipine did not affect the free plasma levels of the antiepileptics. These data indicate that the opposite actions of niguldipine alone or combined with carbamazepine (or phenobarbital) were not associated with Ca(2+) channel blockade. The present results may argue against the use of niguldipine as an adjuvant antiepileptic or for cardiovascular reasons in patients with complex partial seizures.

Gonadotropin subunit transcriptional responses to calcium signals in the rat: evidence for regulation by pulse frequency.

Alterations in the frequency of calcium influx signals to rat pituitary cells can regulate the expression of gonadotropin subunit mRNAs in a differential manner, producing effects that are similar to those previously found for GnRH. The present study was conducted to investigate whether this reflects a transcriptional response to calcium pulse frequency, as determined by alterations in primary transcript (PT) expression. Perifused rat pituitary cells were given pulses of the calcium channel-activator Bay K 8644 (BK; with 10 mM KCl in the injectate) for 6 h. The response to alterations in pulse dose was examined by giving pulses of 1, 3, or 10 microM BK at 60-min intervals. Maximal increases in LHbeta and FSHbeta PTs were obtained with the 3-microM BK pulse dose and with the 10-microM dose for alpha. To investigate the effect of calcium pulse frequency, 3-microM BK pulses were given at intervals of 15, 60, or 180 min. Alpha PT was selectively stimulated by 15-min pulses and LHbeta by 15- and 60-min pulses of BK. In contrast, FSHbeta PT was maximally stimulated by the slower, 180-min pulse interval. These findings reveal that pulsatile increases in intracellular calcium stimulate alpha, LHbeta, and FSHbeta transcription in a differential manner. Thus, intermittent changes in intracellular calcium appear to be important in the transmission of GnRH pulse signals from the plasma membrane to the gene, and they may mediate the differential actions of pulse frequency on gonadotropin subunit gene expression.

Presynaptic L-type Ca(2)+ channels on excessive dopamine release from rat caudate putamen.

We investigated by means of behavioral and neurochemical studies the role of the nerve terminal L-type voltage sensitive Ca(2)+ channel on dopamine (DA) release. Microinjection of Bay K 8644 (BAYK), an L-type Ca(2)+ channel stimulant, into the rat caudate putamen increased locomotor activity and rearing behavior in a dose-dependent manner, whereas injections into the amygdala had no effect. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Significant increases of extracellular DA levels were detected by microdialysis 20 min after BAYK administration into caudate putamen and then declined. This increase was influenced by tetrodotoxin, an axonal Na(+) channel blocker. Pretreatment with nimodipine and nicardipine, but not nifedipine, which are 1, 4-dihydropyridine L-type Ca(2)+ channel antagonists, administered into the caudate putamen significantly blocked BAYK-induced hyperactivity and DA efflux. These results indicate that the extraordinary DA release in the caudate putamen was mediated by extreme stimulation of the nicardipine and nimodipine-sensitive L-type Ca(2)+ channel present in the nerve terminal of striatal DA neurons.

Effects of calcium channel ligands on anaesthetic properties of ethanol in mice.

This study has examined the effect of two calcium channel antagonists--nifedipine, verapamil and a calcium channel agonist BAY K 8644 on duration of ethanol-induced anaesthetic activity measured as the loss of the righting reflex (LORR) in mice. Nifedipine (5 and 10 mg/kg, i.p.) and verapamil (10 and 20 mg/kg, i.p.) potentiated the acute general anaesthetic effect of ethanol (3.5 g/kg, i.p.). BAY K 8644 (2 mg/kg, i.p.) shortened the duration of ethanol-induced LORR. This action of BAY K 8644 was prevented by the pretreatment with nifedipine (2.5 mg/kg, i.p.) but not with verapamil (5 mg/kg, i.p.). Injections of both calcium channel blockers--nifedipine (2.5 mg/kg) and verapamil (5 mg/kg) did not influence the ethanol-induced hypnotic activity themselves. Our results suggest that the calcium ions are involved in the central depressant effects of acute ethanol administration at high doses. It can be supposed that the modification of the activity of voltage-dependent calcium channels plays an important role in the anaesthetic action of ethanol.

A calcium agonist, Bay k 8644, suppresses the embryotoxic effects induced by dihydropyridines calcium channel blockers in cultured rat embryos.

Day 9 rat embryos were exposed to 1,4-dihydropyridine calcium channel blockers; nifedipine (NIF), nicardipine (NIC) or nitrendipine (NIT), for 48 hr in the whole embryo culture system. There were dose-dependent growth retardation and abnormalities, predominantly in cardiovascular system. The three compounds exhibited very similar pattern of dysmorphogenic effects, but the potency of these compounds were quantitatively different. The incidences of embryos with the abnormalities were 100%, 100% and 85% following either exposure of NIF, NIC or NIT at concentration of 300, 8 and 15 microM, respectively. This study was to investigate whether these blocker-induced embryotoxicity was due to calcium channel blocking properties themselves in the embryos. Day 9 rat embryos were co-exposed to 1,4-dihydropyridine calcium channel agonist, Bay k 8644 (BAY) and each calcium channel blocker under the same culture condition. The retarded embryonic growth induced by 200 or 300 microM of NIF, 8 microM of NIC and 15 microM of NIT nearly of completely ameliorated when embryos were co-exposed with BAY at one-third or half concentration of each calcium channel blocker. Supplementation of BAY reduced the incidence of abnormalities by NIF-, NIC- and NIT-alone. These results suggested that one of mechanisms for embryotoxicity induced by calcium channel blocker was directly related to channel blocking property of the chemicals.

Influence of isradipine, niguldipine and dantrolene on the anticonvulsive action of conventional antiepileptics in mice.

We report the effects of two new dihydropyridine derivatives, isradipine (4-(4'-benzofurazanyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinedic arboxylic acid methylisopropylester) and niguldipine (1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinecarboxylic acid 3-(4,4-diphenyl-1-piperidinyl)-propyl methyl ester hydrochloride), and of dantrolene (1-[(5-[p-nitrophenyl]furfurylidene)-amino]hydantoin sodium, an inhibitor of Ca2+ release from intracellular stores) on the protective efficacy of antiepileptic drugs against maximal electroshock-induced seizures. It was shown that dantrolene (5-20 mg/kg), isradipine (5-10 mg/kg) and niguldipine (up to 2.5 mg/kg) did not influence the electroconvulsive threshold in mice, although a higher dose of niguldipine (5 mg/kg) significantly elevated it. Dantrolene (10-20 mg/kg) and isradipine (1 mg/kg) did not affect the anticonvulsive activity of conventional antiepileptic drugs. In contrast, niguldipine (2.5-5 mg/kg) impaired the protective action of carbamazepine and phenobarbital. No effect of niguldipine (2.5-5 mg/kg) was observed upon the anticonvulsive efficacy of diphenylhydantoin and valproate. BAY k-8644 (methyl-1,4-dihydro-2,6-dimethyl-5-nitro-4- [(2-trifluoromethyl)-phenyl]-pyridine-5-carboxylate, an L-type Ca2+ channel agonist) did not reverse the action of niguldipine alone or the niguldipine-induced impairment of the anticonvulsive action of carbamazepine and phenobarbital. Niguldipine did not influence the free plasma levels of carbamazepine and phenobarbital, so a pharmacokinetic interaction is not probable. The results suggest that in contrast to the anticonvulsive activity of niguldipine against electroconvulsions, this Ca2+ channel inhibitor significantly weakened the protective action of both carbamazepine and phenobarbital. These effects do not seem to result from the blockade of voltage-dependent Ca2+ channels. Isradipine and dantrolene did not have a modulatory action on the threshold for electroconvulsions or on the anticonvulsive activity of antiepileptic drugs. It may be concluded that the use of niguldipine, isradipine, and dantrolene in epileptic patients seems questionable.

Rhythmic relaxations of active tension in the rabbit large arteries induced by a combination of cyclopiazonic acid and Bay K 8644.

1. We previously demonstrated that cyclopiazonic acid (CPA), an inhibitor of Ca(2+)-ATPase in the sarcoplasmic reticulum, induced rhythmic relaxations of active tension in the endothelium-denuded small arteries of the mesentery and the ear of the rabbit, but that this agent failed to induce rhythmic responses in the endothelium-denuded rabbit femoral artery. 2. In the present study, an attempt was made to induce rhythmic relaxations of active tension in the endothelium-denuded rabbit femoral artery and the thoracic aorta, both of which were suspended in organ chambers for isometric tension recordings, by using CPA plus Bay K 8644, an L-type Ca2+ channel agonist, to induce an excessive increase in cytosolic Ca2+. 3. CPA or Bay K 8644 alone failed to produce rhythmic relaxations in the femoral artery that had been contracted with phenylephrine. In contrast, rhythmic responses were induced by the sequential treatment of the femoral artery with CPA and Bay K 8644. 4. The rhythmic relaxations of active tension in the femoral artery induced by CPA plus Bay K 8644 were inhibited by charybdotoxin and by iberiotoxin, both of which are antagonists of the Ca(2+)-activated K+ channel, but not by glibenclamide, a blocker of the ATP-sensitive K+ channel. 5. The endothelium-denuded rabbit aorta also exhibited rhythmic responses by the sequential addition of CPA and Bay K 8644. These responses were sensitive to charybdotoxin. 6. These findings indicate that, like small arteries, the large femoral and aortic arteries of the rabbit are also capable of displaying rhythmic relaxations of active tension; these relaxations may be in part attributed to the activation of the Ca(2+)-activated K+ channel as a result of the Ca2+ overload caused by CPA and Bay K 8644.

Effects of cerebral ischemia on N-methyl-D-aspartate and dihydropyridine-sensitive calcium currents. An electrophysiological study in the rat hippocampus in situ.

BACKGROUND AND PURPOSE: During cerebral ischemia, both promoting and limiting factors are present for activation of the N-methyl-D-aspartate (NMDA) receptor ion channel and the dihydropyridine (DHP)-sensitive Ca2+ channels. We investigated the activity of these channels during ischemia and reperfusion in the rat hippocampus in situ. METHODS: Reversible ischemia was induced by bilateral carotid artery ligation. NMDA and BAY K8644 were applied by iontophoresis or pneumatic ejection, and extracellular field potential and resistance changes were recorded from the CA1 region of the rat hippocampus. Resting membrane potentials of the CA1 neurons were also recorded. RESULTS: DC potential shifts produced by NMDA and BAY K8644 were reduced when ischemia depressed the evoked activity more than 50%. They disappeared on total failure of synaptic transmission and recovered during reperfusion. When the evoked activity was depressed less than 50%, DC shifts were greater than their preischemic values; however, BAY K8644-induced potentiation did not reach statistical significance. CA1 neurons were depolarized during ischemia. CONCLUSIONS: These data suggest that ischemia severe enough to cause transmission failure inactivates NMDA and DHP-sensitive Ca2+ currents. During less intense ischemia and reperfusion, NMDA and DHP-sensitive Ca2+ channels are functional, and their overactivation may lead to neurotoxicity.

Effects of Bay K 8644 in aorta from spontaneously hypertensive and Wistar Kyoto rats of different ages.

1. The Ca(2+)-channel agonist, Bay K 8644, induced small contractions in aortae from Wistar-Kyoto (WKY) rats of 5-week-, 3-month-, 1-year- and 1.5-year-old, which were unaltered with age. These contractions were increased by partial depolarization with 15 mM K+. 2. In segments from spontaneously hypertensive rats (SHR), the contractions obtained in both situations were similar and equivalent to those observed in segments from normotensive animals partially depolarized. Responses to Bay K 8644 were modified by age only in tissues from the SHR, the responses to this agent in basal conditions being increased in tissues from 3-month- and 1-year-old animals and depressed in those from 1.5-year SHR. 3. A reduction of the response to Bay K 8644 was observed in partial depolarized endothelium denuded segments from WKY of all ages, and no modification in basal situation. However, the direct contractions induced by Bay K 8644 in aortae from 3-month- and 1.5-year-old SHR were reduced by endothelium removal. 4. These results suggest that: (a) in the hypertensive strain the voltage-gated Ca2+ channels seem to be partially activated; (b) the direct contractions induced by Bay K 8644 were unaltered by age in aortae from WKY but increased in tissues from SHR of 3-month-and-1-year old and depressed in those from 1.5 years, and (c) the contractions evoked by Bay K 8644 seem to involve an endothelium-derived contracting factor in aortae from both strains, or the endothelium produces a partial depolarization of vascular smooth muscle that increases the responsiveness to Bay K 8644.

Evidence that L-type calcium channels do not contribute to static vestibular function in the guinea pig vestibular nucleus.

Labyrinthine-intact guinea pigs received unilateral, brainstem cannula injections of (1) 2.5 micrograms of the selective dihydropyridine L-type Ca2+ channel agonist, Bay K 8644 (n = 4 animals); (2) 10 micrograms Bay K 8644 (n = 4); 12.5 micrograms of the selective dihydropyridine L-type Ca2+ channel antagonist, nifedipine (n = 4); or 40 micrograms nifedipine (n = 4). In 11/16 cases, the lesion associated with the cannula tip was located within or near the border of the right vestibular nucleus (VN) complex. All cannula injections were delivered in a 1 microliter volume of artificial cerebrospinal fluid (ACSF) and dimethylsulphoxide (DMSO) (70% DMSO, 30% ACSF for Bay K 8644; 80% DMSO, 20% ACSF for nifedipine), adjusted to a pH of approx. 7.0. The effects of these injections were compared with control injections of ACSF/DMSO in our previous studies. Animals were observed for signs of a labyrinthine syndrome (i.e. spontaneous ocular nystagmus, yaw and roll head tilt) directed to the contralateral or ipsilateral side. In no case did Bay K 8644 or nifedipine cause ocular motor or postural symptoms similar to those produced by a unilateral labyrinthectomy. These results suggest that L-type Ca2+ channels do not contribute significantly to the resting activity of VN neurons and therefore do not contribute to static vestibular function at the level of the VN.

Effects of halothane and isoflurane on cytosolic calcium ion concentrations and contraction in the vascular smooth muscle of the rat aorta.

BACKGROUND: Halothane and isoflurane have been reported to suppress the contraction of vascular smooth muscle, although the exact mechanism has not been explained fully. This study examined the effect of halothane and isoflurane on cytosolic calcium ion (Ca2+) concentrations ([Ca2+]cyt), which was measured simultaneously with muscle tension in the vascular smooth muscle of the rat aorta to improve the understanding of the anesthetic's effect on vascular smooth muscle. METHODS: Isolated spiral strips of rat thoracic aorta were suspended for isometric tension recordings in physiologic salt solution. The [Ca2+]cyt was measured concomitantly by using fura-2-Ca2+ fluorescence. During exposure to 0%, 1%, 2%, or 3% halothane or 0%, 2%, or 4% isoflurane, increases in muscle tension and [Ca2+]cyt induced by 32.8 mM K+ or 30 nM norepinephrine were measured and compared with the reference values. In the other series, the 3% halothane-induced increase in [Ca2+]cyt was measured in Ca2+)-free solution without and with a pretreatment of ryanodine, caffeine, or norepinephrine. RESULTS: Halothane and isoflurane increased resting-state [Ca2+]cyt, although only 3% halothane elicited a transient increase in muscle tension during the resting state. By contrast, both anesthetic agents attenuated the high K(+)- and norepinephrine-induced increases in [Ca2+]cyt and muscle tension in a concentration-dependent manner. During 3% halothane or 4% isoflurane exposure, the pretreatment of the muscle strip with a 10(-6)-M dose of Bay K 8644 augmented the high K(+)-induced increase in [Ca2+]cyt to the level observed in the control (0% anesthetic exposure) state. However, the increase in muscle tension in the presence of Bay K 8644 was low; it was still attenuated from the control level during 3% halothane or 4% isoflurane administration. These results indicate that, not only [Ca2+]cyt-dependent, but also [Ca2+]cyt-independent, mechanisms are involved in the anesthetic-induced suppression of smooth muscle contraction. A 3% halothane-induced increase in [Ca2+]cyt was observed in the Ca(2+)-free solution even when the muscle strip was pretreated with a 10(-6)-M dose of ryanodine and a 20-mM dose of caffeine, whereas it was abolished completely after the muscle strip was pretreated with ryanodine, caffeine, and 100 nM norepinephrine. These results indicate that halothane can release Ca2+ from an intracellular Ca2+ store other than the caffeine-releasable site. CONCLUSIONS: Halothane and isoflurane have multiple effects on the [Ca2+]cyt and induce [Ca2+]cyt-dependent and [Ca2+]cyt-independent suppression of the contraction in the vascular smooth muscle.

Canine left ventricular hypertrophy predisposes to ventricular tachycardia induction by phase 2 early afterdepolarizations after administration of BAY K 8644.

OBJECTIVES: The purpose of this study was to test the hypothesis that the longer duration of ventricular action potentials in hypertrophied hearts predisposes to the development of early after-depolarizations and triggered ventricular tachyarrhythmias. BACKGROUND: For unknown reasons, the incidence of sudden death is greater in patients with myocardial hypertrophy. METHODS: We measured left ventricular monophasic action potentials in normal dogs and dogs with left ventricular hypertrophy before and after administration of the calcium agonist BAY K 8644 and the potassium channel blocker cesium. RESULTS: We demonstrated longer action potential durations in dogs with than in those without left ventricular hypertrophy. Also, BAY K 8644 produced phase 2 early afterdepolarizations and ventricular tachyarrhythmias more frequently in the dogs with than in those without left ventricular hypertrophy. Phenylephrine, an alpha agonist, further increased the action potential duration in hypertrophied hearts and the propensity to develop early afterdepolarizations and ventricular tachyarrhythmia after administration of BAY K 8644. Control and hypertrophied hearts developed early afterdepolarizations and ventricular tachyarrhythmia equally when exposed to cesium. CONCLUSIONS: Although in vitro studies have shown that fibers of hypertrophied ventricular myocardium can develop triggered activity as a result of both early and late afterdepolarizations, the present study is the first to show in vivo that the hypertrophied ventricular myocardium compared with the normal ventricle is predisposed to develop phase 2 early afterdepolarizations that appear to trigger ventricular tachyarrhythmia. It is possible that such a mechanism contributes to the development of ventricular tachyarrhythmia and sudden cardiac death in patients with left ventricular hypertrophy. If this is shown to be true, specific pharmacologic interventions can be suggested.

Bay K-8644 in different solvents acts as a transient calcium channel antagonist and a long-lasting calcium channel agonist.

This report describes the effect of Bay K-8644 dissolved in various solvents on two types of calcium channel currents in neuroblastoma cells. Transient calcium channel (T channel) currents were not affected by Bay K-8644 dissolved in ethanol (EtOH) or polyethylene glycol (PEG). However, at the same concentration of 0.6 microM, Bay K-8644 dissolved in dimethylsulfoxide (DMSO) (Bay K-8644/DMSO) decreased the T channel current by 50%. The concentration of all three solvents in the bath was fixed at 0.3% to reach different final concentrations of Bay K-8644. At this fixed solvent concentration, the inhibitory effect of Bay K-8644/DMSO on T channel currents was dose-dependent; the solvents alone did not have any effect on T channel currents; and DMSO pretreatment of cells did not render the T channel current sensitive to Bay K-8644 dissolved in EtOH or PEG. Bay K-8644/DMSO was dried using a flash evaporator and redissolved in EtOH or PEG. Dried Bay K-8644 that was redissolved in EtOH or PEG to achieve a final concentration of 0.6 microM inhibited T channel currents by 39 or 35%, respectively. Furthermore, Bay K-8644 (10 nM) increased L channel currents by 80% with DMSO, but only 30% with EtOH as the solvent. These results show that in neuroblastoma cells Bay K-8644/DMSO, within the concentration range examined, is a T channel antagonist and more effective L channel agonist than Bay K-8644 dissolved in the two other solvents.

BAY K 8644 stimulates glucose-dependent rise of cytoplasmic Ca2+ in hyperpolarized pancreatic beta-cells.

The effect of BAY K 8644 on the cytoplasmic Ca2+ concentration ([Ca2+]i) was studied in pancreatic beta-cells hyperpolarized by the K+ channel-activating agent diazoxide. After 50-60 min preexposure to 0-20 mM glucose in the presence of 400 microM diazoxide [Ca2+]i was close to the level in unstimulated beta-cells. The addition of 5 microM BAY K 8644 then triggered a rise of [Ca2+]i dependent on Ca2+ influx. The magnitude of the BAY K 8644 effect increased with the glucose concentration and was almost 10-fold higher in 20 mM than in the absence of the sugar. It is concluded that glucose can modulate Ca2+ entry through the voltage-dependent channels by a mechanism additional to depolarization. This action may help to explain why previous exposure to the sugar results in an augmented insulin response to a second challenge.

Effects of intracoronary administration of endothelin in anesthetized dogs: comparison with Bay k 8644 and U 46619.

The effects of synthetic endothelin on the coronary circulation were studied in pentobarbital-anesthetized dogs and compared with those of Bay k 8644, a dihydropyridine calcium channel agonist, and U 46619, a thromboxane analogue. Intracoronary bolus administration of endothelin reduced coronary blood flow and increased coronary arterial resistance. Similarly, intracoronary bolus administration of equipotent doses of Bay k 8644 or U 46619 significantly reduced coronary blood flow and increased coronary arterial resistance. The coronary vasoconstrictor effects of endothelin were long-lasting as compared with the transient actions of Bay k 8644 and U 46619. Intracoronary bolus injection of endothelin also reduced left ventricular (LV) dP/dt arterial pressure (MAP), and cardiac output (CO). In contrast, Bay k 8644 increased LVdP/dt but did not alter CO or MAP. Intracoronary bolus injection of U 46619 did not affect MAP, CO, or LVdP/dt. In a separate group of animals, intracoronary infusion of nitrendipine significantly increased coronary blood flow and reduced coronary arterial resistance. Other cardiovascular parameters measured were not significantly altered. In the presence of nitrendipine, the effects of intracoronary administration of endothelin and U 46619 on coronary blood flow, coronary arterial resistance, and LVdP/dt were only partially antagonized. On the other hand, the effects of Bay k 8644 were completely prevented in the presence of nitrendipine. These studies show that at doses which reduce coronary blood flow to the same extent, only endothelin produces myocardial depression in anesthetized dogs. The cardiovascular actions of endothelin were only partially antagonized by nitrendipine, suggesting that mechanisms other than calcium influx through voltage-operated channels are involved.