Activation of protein kinase C by the dihydropyridine calcium channel blocker, felodipine

Felodipine, a dihydropyridine Ca2+ channel blocker, appears to have intracellular sites of action in addition to its ability to attenuate voltage-dependent Ca2+ channels in smooth muscle cells. In vitro, felodipine inhibits several calmodulin-dependent enzymes such as myosin light chain kinase, cyclic nucleotide phosphodiesterase and caldesmon kinase [Walsh MP, Sutherland C and Scott-Woo GC, Biochem Pharmacol 37: 1569-1580, 1988]. Such effects may partially explain the relaxant effects of felodipine and related dihydropyridines on vascular smooth muscle. We have examined the effects of felodipine on the activity of another important enzyme which has been implicated in the regulation of the contractile state of smooth muscle, protein kinase C. We chose to use a physiologically relevant substrate of protein kinase C for these studies, viz. platelet P47 protein, rather than the more commonly used lysine-rich histone which is probably not a physiologically important substrate. Protein kinase C and P47 were purified from human platelets and their important structural and functional properties were characterized. Felodipine and the p-chloro analogue of felodipine enhanced both the rate and extent of P47 phosphorylation by protein kinase C. Half-maximal activation was observed at 9.5 microM felodipine and 8.5 microM p-chloro analogue. Activation by felodipine was dependent upon the presence of phospholipid but did not require diacylglycerol. These observations suggest that the pharmacological actions of felodipine and related dihydropyridines may involve activation of protein kinase C in addition to their known effects on voltage-dependent Ca2+ channels and calmodulin-dependent enzymes.     

Adrenalectomy potentiates the anti-inflammatory activity of a calcium channel blocker

Calcium movement is important in the activation of inflammatory cells. Prior studies have shown that calcium channel blockers (CCBs) inhibit carrageenan-induced paw edema in rats by acting at pituitary and hypothalamic levels. Here we evaluated the role of calcium channel blockers and their regulation via the hypothalamus-pituitary-adrenal (HPA) axis in acute and chronic models of rat paw inflammation, using both carrageenan (acute) and formalin (chronic) as inflammation inducers. Adrenalectomized (ADX) and intact Sprague Dawley rats (n = 4 per group) weighing 150-250 each were treated with an intraperitoneal injection of nifedipine (400 microg/kg) or vehicle. Edema was assessed plethysmometrically by evaluating paw volume changes. The results show a significant contradiction between acute and chronic inflammation data. In intact animals, nifedipine demonstrated a significant anti-inflammatory effect in the acute inflammatory model but not in the chronic model. In adrenal-ectomized animals, the anti-inflammatory effect of nifedipine was significantly enhanced both in acute and chronic models. We conclude that adrenalectomy plays a significant role in modulating the inflammatory pathway in the presence of calcium channel blockers.     

Effects of felodipine (a dihydropyridine calcium channel blocker) and analogues on calmodulin-dependent enzymes

We have examined the effects on the activities of three calmodulin-dependent enzymes (cAMP phosphodiesterase, caldesmon kinase and myosin light chain kinase) of the dihydropyridine Ca2+ channel blocker felodipine and three analogues (p-chloro, oxidized and t-butyl) exhibiting different pharmacological potencies. The cAMP phosphodiesterase was inhibited completely by felodipine and the p-chloro analogue with IC50 values of 3.7 and 1.5 microM respectively. The oxidized and t-butyl analogues were relatively ineffective in inhibiting cAMP phosphodiesterase. Felodipine and the p-chloro analogue inhibited the basal (Ca2+/calmodulin-independent) activity of cAMP phosphodiesterase as well as the calmodulin-stimulated activity. Calmodulin was relatively ineffective in preventing inhibition of cAMP phosphodiesterase by felodipine and the p-chloro analogue. These observations suggest that felodipine may act directly on the phosphodiesterase as well as through calmodulin. Felodipine and the p-chloro analogue inhibited Ca2+/calmodulin-dependent caldesmon kinase with similar potencies (IC50 = 17.4 microM), whereas the oxidized and t-butyl analogues caused no inhibition. Similarly, felodipine and the p-chloro analogue inhibited myosin light chain kinase activity whether the isolated 20 kD light chain (IC50 = 12.6 microM) or intact myosin (IC50 = 11.0 microM) was used as substrate. Inhibition in each case was prevented by excess calmodulin. The oxidized and t-butyl derivatives caused little or no inhibition. Finally, the effects of felodipine and the three analogues on two processes which are dependent on myosin phosphorylation were examined, namely the actin-activated Mg2+-ATPase activity of myosin and the assembly of myosin filaments. Felodipine and the p-chloro analogue inhibited the actin-activated Mg2+-ATPase activity of smooth muscle myosin (IC50 = 25.1 microM). The oxidized and t-butyl analogues exhibited no inhibition. Similarly, felodipine and the p-chloro analogue blocked myosin filament assembly induced by low concentrations of calmodulin, whereas the oxidized and t-butyl analogues did not. Again, inhibition of the actin-activated myosin Mg2+-ATPase and myosin filament assembly by felodipine and the p-chloro analogue could be reversed by raising the calmodulin concentration. These observations suggest that some of the pharmacological actions of felodipine on smooth muscle may involve inhibition of calmodulin-dependent enzymes which are functionally involved in the regulation of smooth muscle contraction.     

Metabolism and pharmacokinetics of barnidipine hydrochloride,a calcium channel blocker,in man following oral administration of its sustained release formulation

1. The metabolism and pharmacokinetics of barnidipine hydrochloride, a 1,4- dihydropyridine calcium antagonist,were evaluated following single oral administration of a sustained release formulation (SR) capsule comprising of quick and slow release pellets to healthy male volunteers. 2. Various metabolites were identified and quantitated by newly established GC-MS analytical methods. Major metabolites were the hydrolyzed product of the benzylpyrrolidinyl ester (M-3) in plasma and its oxidized pyridine product (M-4) in plasma and urine. The pyridine form ofunchanged barnidipine and the N -debenzylated product were observed as minor metabolites. Therefore, the primary metabolic pathways in man are (a) hydrolysis of the benzylpyrrolidine ester, (b) N -debenzylation, and (c) oxidation of the dihydropyridine ring. 3. When the SR and normal capsules were administered at a dose of 10?mg to six subjects in a crossover design, AUC of unchanged drug, M-3 and 4 in each subject receiving the SR were 97 15, 85 31 and 76 21% respectively of those subjects receiving the normal formulation. The sum of the excretion of urinary metabolites for the SR formulation was 65 6% of that for the normal formulation. These data suggest that the absorption of the SR formulation is slightly reduced but that its bioavailability is comparable to that of the normal formulation.     

Nasal administration of the calcium channel blocker diltiazem decreases food intake and attenuates weight gain in rats

Food intake is normally influenced by a multitude of complex endogenous neurochemical systems, in addition to numerous external environmental stimuli, including olfaction. Since most olfactory neurons process odorant exposures through Ca2+-mediated mechanisms via Ca2+ channels, a novel approach at influencing the ingestive behaviors of animals might therefore involve altering olfactory acuity via Ca2+ channel blockade. We tested the ability of a Ca2+ channel blocker, diltiazem, to alter food intake in hyperphagic rats when administered using the intranasal (i.n.), intraperitoneal (i.p.), oral (p.o.) or intracerebroventricular (i.c.v.) routes of administration. Male Sprague Dawley rats, which had been food-deprived for 4 h at the beginning of the dark cycle, were administered different doses of diltiazem (0-8 mg/animal or 0-40 mg/kg) and the amounts of food consumed were measured. While food intake at 1, 2 and 4 h post drug administration was significantly decreased in a dose-dependent manner after i.n. administration, the i.p., p.o., and i.c.v. routes did not affect food intake. In another experiment, rats trained to eat their daily meal during the first 4 h at the onset of the dark cycle and treated daily with i.n. diltiazem (0-8 mg/animal) prior to food introduction exhibited a significantly decreased rate of weight gain in a dose-dependent manner over a 14-day period. Both i.n. and i.p. diltiazem significantly increased the plasma drug concentration at 1 h, however there was no significant difference between these routes of administration. Additional studies failed to demonstrate any detrimental effects of i.n. diltiazem (0-8 mg/animal) on conditioned taste aversion, locomotion or gross neurological/behavioral competence using the rota-rod test. While a local action on the nasal odorant receptors is most likely the site of diltiazem's action, further studies are needed to determine the exact mechanism of action of i.n. diltiazem.     

新型钙通道阻滞药依福地平

依福地平是一个新型的钙通道阻滞药,具有同时阻滞L型钙通道和T型钙通道的作用。除治疗高血压外,依福地平尚在延迟慢性肾脏疾病进展、治疗心力衰竭、延迟心房颤动电生理重构、预防肺静脉触发活动中发挥重要作用。     

Renal failure in haemorrhagic shock in dogs: Salutary effects of the calcium entry blocker felodipine

Summary The efficacy of felodipine, a dihydropyridine calcium entry blocker to restore renal function was investigated in Wiggers model of haemorrhagic shock. Mongrel dogs were anaesthetized with sodium pentobarbital and subjected to haemorrhagic shock by allowing the animals to bleed into a reservoir. After maintaining the hypotensive state (mean blood pressure 40–45 mm Hg) for a period of 150 min, the blood was reinfused and the recovery of the various parameters were monitored for an additional 120 min. These studies were conducted in three different groups of dogs: (A) Solvent control, (B) Felodipine 0.01 mol/kg i. v., administered 10 min prior to reinfusion of the blood, and (C) Felodipine 0.01 mol/kg i. v., administered prior to haemorrhage. In all the three groups arterial blood pressure returned to similar basal levels following reinfusion. Felodipine administration prior to haemorrhage or before reinfusion (Group B and C) resulted in a 80–95% recovery in the renal blood flow, 60–65% in the glomerular filtration rate, 15–300% in the urine volume and 80–100% in the urinary sodium and potassium excretions. In the vehicle-treated control group, despite a 45% recovery in the renal blood flow, renal function was not restored following reinfusion.The observations made in these studies suggest that felodipine, an arteriolar dilator which also possesses natriuretic properties, could be clinically useful in the treatment of renal failure in haemorrhagic shock. Prevention of cellular calcium overload during ischaemia and reperfusion by this dihydropyridine derivative, may account for its ability to preserve vascular as well as tubular function. Send offprint requests to B. S. Jandhyala at the above address     

钙通道阻滞剂降压治疗进展

<正> 钙通道阻滞剂(CCB)作为降血压药物家族中的重要一员,临床上已应用多年。本文概要讨论了CCB的分类、降压作用机制、疗效及降压之外的靶器官保护作用的研究进展。 1 CCB的分类钙通道分两类:L型和T型钙通道。L型钙通道在高膜电位2相时开放,开放时间长,心肌细胞、房室结细胞密度较高,主要与房室传导、心肌和血管收缩有关;T型钙通道于低膜电位0相除极时开放,开     

Nifedipine: more than a calcium channel blocker

Nifedipine exhibits a greater incidence of side effects than the other currently marketed calcium channel antagonists. In addition to those effects attributable to calcium channel blockade, nifedipine produces side effects similar to the effects of adenosine. It is probable that nifedipine exerts part of its physiological actions through potentiation of adenosine. Adenosine, an endogenous calcium channel blocker, modifies synaptic events throughout the nervous system and causes sedation, smooth and skeletal muscle relaxation, anticonvulsion, hypotension and hypothermia, all reversible by caffeine or theophylline administration. Nifedipine inhibits adenosine uptake from, and release into, the extracellular space and binds at an adenosine receptor. Both nifedipine and adenosine interact with benzodiazepine binding sites. Interaction between nifedipine and adenosine should be kept in mind when treating patients with nifedipine.     

Chronic administration of the L-type calcium channel blocker nimodipine can facilitate the acquisition of sequence learning in a radial-arm maze

Nimodipine, a dihydropyridine L-type voltage-gated calcium-channel blocker, was examined for its potential effect on the acquisition of a complex-arm sequence task in an automated radial maze. Young (60-day-old) male Wistar rats were injected with saline or nimodipine (5 mg/kg) 15 min prior to radial maze training, or immediately following the radial maze testing. The results of the learning task (over 7 days of testing) showed that rats injected with nimodipine each training session acquired the task more quickly and more efficiently compared to saline-treated animals. There were no significant differences for rats that were pre-/post-treated with nimodipine during the maze-learning task. The number of incorrect arm entries and number of additional lever presses in the same arm were found to be significantly lower in rats treated with nimodipine compared to saline-injected controls. The beneficial effect of nimodipine treatment occurred only in rats that were acquiring the task, and not in rats that had already learned the arm sequence paradigm. There were no potential non-specific influences on locomotor activity or appetite caused by chronic nimodipine treatments. These results strongly suggest that nimodipine can facilitate the acquisition of a complex learning task.     

Effects of the calcium channel blocker nimodipine on nicotine-induced locomotion in rats

The effects of nimodipine, an L-type calcium channel antagonist, on nicotine-induced locomotor activity were investigated in drug-naive rats. Nicotine (0.4 mg/kg IP) produced significant increases in locomotion following acute administration. However, when rats were given injections of nimodipine (5, 10, or 20 mg/kg IP) 1 h prior to the test drug, nicotine-induced locomotor activity was altered. Nimodipine 5 mg did not significantly block locomotor activity produced by nicotine. In contrast, pretreatment with 10 and 20 mg nimodipine significantly blocked nicotine-induced locomotor activity. These findings clearly indicate that nicotine-induced locomotion is altered by nimodipine in a dose-dependent fashion. Results further suggest that the effect of nicotine on locomotion is calcium-dependent.     

A suicide attempt with an oral calcium channel blocker

Calcium channel blockers are widely used in all-aged populations. The drugs are generally safe in therapeutic dosage, but severe side effects with elevated intake are increasingly described, mainly in adult patients. We report an adolescent girl who intentionally ingested an overdose of nifedipine.     

The effect of calcium load and the calcium channel blocker verapamil on gentamicin nephrotoxicity in rats

Gentamicin (GM) is used against serious and life-threatening Gram negative infections. However its use is limited by the occurrence of nephrotoxicity. Reports on the interaction between GM nephrotoxicity and calcium (Ca²⁺) or Ca blockers are conflicting. Therefore, in the present work we assessed the effect of treatment of rats with graded doses of calcium carbonate, CaCO₃ (0.25, 0.5 or 1.0 g/kg) orally, or the Ca²⁺ channel blocker verapamil (1.75, 3.5 or 7.0 mg/ kg) intramuscularly (i.m.), on the nephrotoxicity induced by concomitant i.m. treatment with GM (80 mg /kg/day for 6 days). Nephrotoxicity was evaluated histopathologically by light microscopy and biochemically by measuring the concentrations of urea and creatinine in plasma, reduced glutathione (GSH), lipid peroxidation and superoxide dismutase (SOD) activity in kidney cortex. The results indicated that the administration of CaCO₃ produced a dose-dependent amelioration in the biochemical indices of nephrotoxicity in plasma and renal cortex, which was significant at the two higher doses used. The histological picture of the renal proximal tubules followed a similar pattern. Treatment with verapamil induced a dose-dependent potentiation in the biochemical parameters of nephrotoxicity that was significant only at the highest dose used (7 mg/kg). This dose also exacerbated the GM-induced histological necrosis. The above interactions may be clinically relevant in patients treated concurrently with these agents.     

The binding of the calcium channel blocker, bepridil, to calmodulin

Bepridil had the highest relative potency for inhibition of myosin light chain kinase (MLCK) activated by Ca2+-calmodulin of all the calcium channel blockers we examined. Kinetic analysis indicated that the primary effect of bepridil was mediated through a competitive inhibition of the enzyme activation by interaction with calmodulin and the apparent Ki value of this agent was 2.2 microM. We then examined the binding of bepridil to calmodulin, using the equilibrium column binding technique. [3H]bepridil bound to the calcium-calmodulin complex, but not to calmodulin in the presence of 2 mM EGTA. Scatchard analysis of the binding of bepridil to calmodulin demonstrated that the dissociation constant was 6.2 microM and the calculated number of specific binding sites was about 5 sites per molecule of calmodulin. The concentrations of unlabeled bepridil, W-7, prenylamine, verapamil and diltiazem producing 50% inhibition (IC50) of the binding of [3H]bepridil to calmodulin were 4 microM, 28 microM, 45 microM, 130 microM and 700 microM, respectively. However, nifedipine and nicardipine did not displace [3H]labeled bepridil from calmodulin. There was a good correlation between the displacement of [3H]bepridil from calmodulin and the inhibitory effect on MLCK by these calcium channel blockers and W-7. These results suggest that bepridil binds to calmodulin in the presence of calcium and potently inhibits the phosphorylation of myosin light chain.     

Cardioprotective actions of a new calcium channel blocker in acute myocardial ischemia

The ability of anipamil, a calcium channel blocker, to protect ischemic myocardial tissue was investigated in pentobarbital anesthetized cats. Two bolus injections of anipamil (1.0 mg/kg i.v.) or their vehicle (i.e., 95% ethanol) were given 30 and 150 min post-ligation of the left anterior descending coronary artery. Anipamil significantly reduced the elevated S-T segment elevation and T wave amplitude suggesting a moderating influence on cellular ischemia. The drug also significantly blunted the loss in myocardial creatine kinase activity and amino-nitrogen concentrations from ischemic myocardial tissue, compared to cats receiving only the vehicle. These changes are suggestive of a cardioprotective effect of this calcium channel blocker. Since no significant change in the pressure rate index was seen with anipamil, a decrease in myocardial oxygen demand does not appear to be the major mechanism of the cardioprotective action of the agent. Therefore, anipamil protected the heart from ischemic damage, possibly by a direct cytoprotective action.     

A fatal case of iatrogenic hypercalcemia after calcium channel blocker overdose

We report a case of a 61-year-old woman treated for a suspected verapamil overdose with continuous calcium chloride infusion, resulting in severe hypercalcemia of 32.3 mg/dL (8.07 mmol/L) with a normal range of 8.6–10.5 mg/dL (2.15–2.63 mmol/L). Treatment with acute hemodialysis rapidly normalized the serum calcium level, but the patient later died of vasoconstrictive complications of hypercalcemia.     

Protective effect of t-type calcium channel blocker in histamine-induced paw inflammation in rat

The aim of this paper was to investigate the protective effect of the T-type calcium channel blocker in a model of acute local inflammation (histamine-induced). The intraplantar injection of histamine elicited an inflammatory response that was characterized by a time-dependent increase in paw oedema and neutrophil infiltration in paw tissue. The maximal increase in paw volume was observed at 90 min after histamine administration (maximal paw volume: 0.97 +/- 0.07). In addition, polymorphonuclear leucocyte (PNL) number was markedly increased in the histamine-treated paw tissue (144 +/- 25.56). However, histamine-induced paw oedema was significantly reduced in a dose-dependent manner by treatment with mibefradil (given at 10, 25, 50, and 100 mg x kg(-1)) at 30, 60, 90, 120, 150, 180 min after injection of histamine. Mibefradil treatment also caused a significant reduction of the polymorphonuclear leucocyte number in the paw tissue. Our findings support the view that mibefradil exerts antiinflammatory effects.     

Glucagon in beta-blocker and calcium channel blocker overdoses: a systematic review

BACKGROUND: Glucagon is usually accepted as part of the standard treatment in the management of patients with beta-blocker and calcium channel blocker overdoses. METHODS: A systematic review was done in order to evaluate the evidence supporting glucagon use in beta-blocker and calcium channel blocker overdoses. Studies evaluating glucagon for those uses were identified using the Cochrane Database of Systematic Reviews, the Cochrane Controlled Trials Register, MedLine, ToxLine, and EMBASE searches, as well as reviewing medical toxicology textbooks and references of identified articles. Only controlled studies of human or animal studies were included, the latter only when it was an in vivo model of acute poisoning. The quality of the included studies was assessed. RESULTS: The search found no study in humans but identified 30 in animals. In the five studies of animal models of beta-blocker overdose included, glucagon appeared to consistently increase the heart rate at least transiently but appeared to have no effect on mean arterial pressure even though it possibly increased cardiac output. Its effect on the survival rate in animal models of beta-blocker overdose was unclear. In the six studies of animal models of calcium channel blocker overdose included, glucagon appeared to increase heart rate and cardiac output and reverse second and third degree AV blocks, all at least transiently. There appeared to be no effect of glucagon on mean arterial pressure although it did increase in one model. Glucagon appeared to have no effect on survival rate. The included studies for both overdoses were not blinded, had limited numbers of animals, and some had inadequate glucagon regime. CONCLUSION: The evidence supporting the use of glucagon in the management of patients with beta-blocker and calcium channel blocker overdoses is limited to animal studies.