Residue levels of captan and trichlorfon in field-treated kaki fruits, individual versus composite samples, and after household processing

The dissipation of residue levels of captan and trichlorfon in field-treated kaki crops was studied according to good laboratory practices to propose maximum residue limits (MRLs). Residue levels of captan and trichlorfon were analysed by GC/MS and LC-MS/MS, respectively. Residue levels of captan and trichlorfon permitted one to propose MRLs in kaki of 3 and 5 mg kg(-1), respectively. The behaviour of these residues was also studied after peeling and cooking, and in individual fruits versus composite samples. Residue levels of these compounds for individual fruits suggested that a variability factor up to three could be set for the acute risk assessment. Levels of captan decreased by more than 90% after peeling and completely after cooking. Trichlorfon penetrates into the flesh in a proportion of 70% of the residue at the pre-harvest interval. Cooking resulted in a decrease of 27% of residue levels of trichlorfon.

Bioassay for determining sensitivity to sulfosulfuron on seven plant species

This study presents a bioassay procedure, based on the root and shoot growth parameters, for the determination of the herbicide sulfosulfuron (1-(4,6 dimethoxypyrimidin-2-yl)-3-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonil)urea) sensitivity on seven vegetal species. Plant response to sulfosulfuron was calculated with the equations fitted to the root growth data as a function of the logarithm of the herbicide concentration by non-linear regression and was used to calculate the doses for 10, 30 and 50% inhibition of root growth (EC10, EC30 and EC50). The results indicate that the phytotoxic effect of sulfosulfuron in all the species assayed followed the order: flax > maize > onion > vetch > lepidium sativum > tomato > barley. These species showed phytotoxicity at low levels of sulfosulfuron and flax appeared to be the most susceptible species to sulfosulfuron (0.001 mg/L).

New Classes of AChE Inhibitors with Additional Pharmacological Effects of Interest for the Treatment of Alzheimers Disease

Alzheimer's disease (AD) is associated to a gradual loss of attention and memory that have been associated to impairment of brain cholinergic neurotransmission, particularly a deficit of cholinergic neurons in the nucleus basalis of Meynert. Thus, it is not surprising that the first therapeutic target that has demonstrated therapeutic efficacy on cognition, behaviour and functional daily activities has been the inhibitors of acetylcholinesterase (AChE), i.e. tacrine, donepezil, rivastigmine and galanthamine. But not all inhibitors of AChE have the same potency to block the enzyme and have a different pharmacological profile. For instance, rivastigmine is a dual inhibitor of AChE and butyrylcholinesterase (BuChE), and galanthamine is a mild inhibitor of AChE and an allosteric potentiating ligand of neuronal nicotinic receptors for acetylcholine (nAChRs). In addition, we have recently found that galanthamine has neuroprotective effects by inducing calcium signals and the induction of the antiapoptotic protein Bcl-2. In this frame, we have been synthesizing new tacrine derivatives that keep their ability to inhibit AChE but that interfere with neuronal calcium overloading and prevent apoptosis. Some of these compounds exhibit neuroprotecting properties and thus, could be useful in the treatment of neurodegenerative and ischaemic brain diseases.

Mitochondrial calcium sequestration and protein kinase C cooperate in the regulation of cortical F-actin disassembly and secretion in bovine chromaffin cells

Mitochondria play an important role in the homeostasis of intracellular Ca(2+) and regulate its availability for exocytosis. Inhibitors of mitochondria Ca(2+) uptake such as protonophore CCCP potentiate the secretory response to a depolarizing pulse of K(+). Exposure of cells to agents that directly (cytochalasin D, latrunculin B) or indirectly (PMA) disrupt cortical F-actin networks also potentiate the secretory response to high K(+). The effects of cytochalasin D and CCCP on secretion were additive whereas those of PMA and CCCP were not; this suggests different mechanisms for cytochalasin D and CCCP and a similar mechanism for PMA and CCCP. Mitochondria were the site of action of CCCP, because the potentiation of secretion by CCCP was observed even after depletion of Ca(2+) from the endoplasmic reticulum. CCCP induced a small increase in the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that was not modified by the protein kinase C (PKC) inhibitor chelerythrine. Both CCCP and PMA induced cortical F-actin disassembly, an effect abolished by chelerythrine. In addition, rotenone and oligomycin A, two other mitochondrial inhibitors, also evoked cortical F-actin disassembly and potentiated secretion; again, these effects were blocked by chelerythrine. CCCP also enhanced the phosphorylation of PKC and myristoylated alanine-rich C kinase substance (MARCKS), and these were also inhibited by chelerythrine. The results suggest that the rapid sequestration of Ca(2+) by mitochondria would protect the cell from an enhanced PKC activation and cortical F-actin disassembly, thereby limiting the magnitude of the secretory response.

Calcium entry through L-type calcium channels causes mitochondrial disruption and chromaffin cell death

Sustained, mild K+ depolarization caused bovine chromaffin cell death through a Ca(2+)-dependent mechanism. During depolarization, Ca(2+) entered preferentially through L-channels to induce necrotic or apoptotic cell death, depending on the duration of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) signal, as proven by the following. (i) The L-type Ca(2+) channel activators Bay K 8644 and FPL64176, more than doubled the cytotoxic effects of 30 mm K+; (ii) the L-type Ca(2+) channel blocker nimodipine suppressed the cytotoxic effects of K+ alone or K+ plus FPL64176; (iii) the potentiation by FPL64176 of the K+ -evoked [Ca(2+)](c) elevation was totally suppressed by nimodipine. Cell exposure to K+ plus the L-type calcium channel agonist FPL64176 caused an initial peak rise followed by a sustained elevation of the [Ca(2+)](c) that, in turn, increased [Ca(2+)](m) and caused mitochondrial membrane depolarization. Cyclosporin A, a blocker of the mitochondrial transition pore, and superoxide dismutase prevented the apoptotic cell death induced by Ca(2+) overload through L-channels. These results suggest that Ca(2+) entry through L-channels causes both calcium overload and mitochondrial disruption that will lead to the release of mediators responsible for the activation of the apoptotic cascade and cell death. This predominant role of L-type Ca(2+) channels is not shared by other subtypes of high threshold voltage-dependent neuronal Ca(2+) channels (i.e. N, P/Q) expressed by bovine chromaffin cells.

Calcium-dependent inhibition of L, N, and P/Q Ca2+ channels in chromaffin cells: role of mitochondria

The hypothesis that the buffering of Ca(2+) by mitochondria could affect the Ca(2+)-dependent inhibition of voltage-activated Ca(2+) channels, (I(Ca)), was tested in voltage-clamped bovine adrenal chromaffin cells. The protonophore carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), the blocker of the Ca(2+) uniporter ruthenium red (RR), and a combination of oligomycin plus rotenone were used to interfere with mitochondrial Ca(2+) buffering. In cells dialyzed with an EGTA-free solution, peak I(Ca) generated by 20 msec pulses to 0 or +10 mV, applied at 15 sec intervals, from a holding potential of -80 mV, decayed rapidly after superfusion of cells with 2 microm CCCP (tau = 16.7 +/- 3 sec; n = 8). In cells dialyzed with 14 mm EGTA, CCCP did not provoke I(Ca) loss. Cell dialysis with 4 microm ruthenium red or cell superfusion with oligomycin (3 microm) plus rotenone (4 microm) also accelerated the decay of I(Ca). After treatment with CCCP, decay of N- and P/Q-type Ca(2+) channel currents occurred faster than that of L-type Ca(2+) channel currents. These data are compatible with the idea that the elevation of the bulk cytosolic Ca(2+) concentration, [Ca(2+)](c), causes the inhibition of L- and N- as well as P/Q-type Ca(2+) channels expressed by bovine chromaffin cells. This [Ca(2+)](c) signal appears to be tightly regulated by rapid Ca(2+) uptake into mitochondria. Thus, it is plausible that mitochondria might efficiently regulate the activity of L, N, and P/Q Ca(2+) channels under physiological stimulation conditions of the cell.

Mechanisms of blockade by the novel migraine prophylactic agent, dotarizine, of various brain and peripheral vessel contractility

The novel antimigraineur, dotarizine, inhibited 5-HT (5 hydroxytryptamine)-evoked contractions of rabbit vertebral, aorta, femoral and mesenteric arteries, with IC(50)s of 1.35, 1.40, 0.52 and 1.09 microM, respectively. Flunarizine had little effect on these contractions, while ketanserin was more potent (IC(50)s of 0.17 microM for vertebral, 0.22 microM for aorta, 0.05 microM for femoral and 0.03 microM for mesenteric arteries). At 10 microM, dotarizine caused 40% blockade of K(+)-evoked contractions of rabbit aorta, and 70% inhibition of 5-HT-evoked responses; these values were 30% and 20% for 10 microM flunarizine. Contractions of rabbit aorta elicited by noradrenaline, angiotensin II or prostaglandin F(2alpha) were not affected by 10 microM dotarizine or flunarizine. Ketanserin shifted to the right, in parallel, the concentration-response curves for 5-HT in rabbit aorta; however, dotarizine caused a non-competitive type of blockade, increasing the maximum 5-HT contraction at 30 nM and decreasing it at 3 and 30 microM. K(+)-evoked contractions of rabbit aorta were halved by 3 microM dotarizine in a voltage-independent manner; flunarizine caused a delayed-type, non-reversible post-drug blockade, and exhibited some voltage-dependence. Blockade by nifedipine was voltage-dependent and fully reversible. Ca(2+)-evoked contractions of depolarised bovine middle cerebral arteries were blocked by 1--3 microM dotarizine in a non-surmountable manner. Contraction of these vessels evoked by electrical stimulation was blocked 50% and 70% by 1 and 3 microM dotarizine, respectively. Dotarizine (1--3 microM) also inhibited to a similar extent the K(+)-evoked [(3)H]noradrenaline release from cultured rat sympathetic neurones. These data suggest that the mechanism of blockade by dotarizine of cerebral vessels contractility has three components: (i) presynaptic inhibition of noradrenaline release; (ii) blockade of postsynaptic vascular 5-HT receptors; (iii) blockade of Ca(2+)entry into the vascular smooth muscle cell cytosol. The compound does not affect the vascular receptors for noradrenaline, angiotensin II or prostaglandin F(2alpha).

The Escherichia coli trmE (mnmE) gene, involved in tRNA modification, codes for an evolutionarily conserved GTPase with unusual biochemical properties

The evolutionarily conserved 50K protein of Escherichia coli, encoded by o454, contains a consensus GTP-binding motif. Here we show that 50K is a GTPase that differs extensively from regulatory GTPases such as p21. Thus, 50K exhibits a very high intrinsic GTPase hydrolysis rate, rather low affinity for GTP, and extremely low affinity for GDP. Moreover, it can form self-assemblies. Strikingly, the 17 kDa GTPase domain of 50K conserves the guanine nucleotide-binding and GTPase activities of the intact 50K molecule. Therefore, the structural requirements for GTP binding and GTP hydrolysis by 50K are without precedent and justify a separate classification in the GTPase superfamily. Immunoelectron microscopy reveals that 50K is a cytoplasmic protein partially associated with the inner membrane. We prove that o454 is allelic with trmE, a gene involved in the biosynthesis of the hypermodified nucleoside 5-methylaminomethyl-2-thiouridine, which is found in the wobble position of some tRNAs. Our results demonstrate that 50K is essential for viability depending on the genetic background. We propose that combination of mutations affecting the decoding process, which separately do not reveal an obvious defect in growth, can give rise to lethal phenotypes, most likely due to synergism.

PF9404C, a new slow NO donor with beta receptor blocking properties

1. PF9404C is the S-S diesteroisomer of a novel blocker of beta adrenergic receptors with vasodilatory properties. It causes a concentration-dependent relaxation of rat aorta helical strips pre-contracted with 10(-6) M noradrenaline (NA; IC(50) 33 nM). It was equipotent to nitroglycerin (NTG; IC(50) 49 nM), but much more potent than isosorbide dinitrate (ISD; IC(50) 15,000 nM). 2. Oxyhaemoglobin (10 microM) shifted to the right the concentration-response curve for the relaxation induced by PF9404C (IC(50) 530 nM) or NTG (IC(50) 61 nM). 3. Either methylene blue (MB) or ODQ (1 microM each) largely prevented the vasorelaxing responses to increasing concentrations of PF9404C or NTG. 4. In rat aorta smooth muscle cells, PF9404C increased the formation of cyclic GMP from 3 pmol mg(-1) protein in basal conditions, to 53 pmol mg(-1) protein in 10 microM PF9404C. Neither metoprolol nor carvedilol enhanced cyclic GMP. 5. In the electrically driven guinea-pig left atrium, PF9404C blocked the inotropic effects of isoprenaline in a concentration-dependent manner. Its IC(50) (30 nM) was similar to that for S-propranolol (22.4 nM) and lower than the IC(50)s for metoprolol (120 nM) and atenolol (192 nM). The beta-adrenergic ligand (-)-[(3)H]-CGP12177 (0.2 nM) was displaced from its binding to rat brain membranes with K(i) of 7 nM, 17 nM, 170 nM and 1.2 microM respectively for PF9404C, S-(-)propranolol, metoprolol, and atenolol. 6. The data are consistent with the idea that the S-S diesteroisomer PF9404C, is a potent vasorelaxing agent, as well as a blocker of cardiac beta adrenergic receptors. The mechanism of its vasorelaxing effects involves the slow generation of NO. This molecule can, therefore, exhibit antihypertensive and cardioprotective actions through a double mechanism, NO donation and beta blockade.

Voltage inactivation of Ca2+ entry and secretion associated with N- and P/Q-type but not L-type Ca2+ channels of bovine chromaffin cells

1. In this study we pose the question of why the bovine adrenal medullary chromaffin cell needs various subtypes (L, N, P, Q) of the neuronal high-voltage activated Ca2+ channels to control a given physiological function, i.e. the exocytotic release of catecholamines. One plausible hypothesis is that Ca2+ channel subtypes undergo different patterns of inactivation during cell depolarization. 2. The net Ca2+ uptake (measured using 45Ca2+) into hyperpolarized cells (bathed in a nominally Ca2+-free solution containing 1.2 mM K+) after application of a Ca2+ pulse (5 s exposure to 100 mM K+ and 2 mM Ca2+), amounted to 0.65 +/- 0.02 fmol cell-1; in depolarized cells (bathed in nominally Ca2+-free solution containing 100 mM K+) the net Ca2+ uptake was 0.16 +/- 0.01 fmol cell-1. 3. This was paralleled by a dramatic reduction of the increase in the cytosolic Ca2+ concentration, [Ca2+]i, caused by Ca2+ pulses applied to fura-2-loaded single cells, from 1181 +/- 104 nM in hyperpolarized cells to 115 +/- 9 nM in depolarized cells. 4. A similar decrease was observed when studying catecholamine release. Secretion was decreased when K+ concentration was increased from 1.2 to 100 mM; the Ca2+ pulse caused, when comparing the extreme conditions, the secretion of 807 +/- 35 nA of catecholamines in hyperpolarized cells and 220 +/- 19 nA in depolarized cells. 5. The inactivation by depolarization of Ca2+ entry and secretion occluded the blocking effects of combined omega-conotoxin GVIA (1 microM) and omega-agatoxin IVA (2 microM), thus suggesting that depolarization caused a selective inactivation of the N- and P/Q-type Ca2+ channels. 6. This was strengthened by two additional findings: (i) nifedipine (3 microM), an L-type Ca2+ channel blocker, suppressed the fraction of Ca2+ entry (24 %) and secretion (27 %) left unblocked by depolarization; (ii) FPL64176 (3 microM), an L-type Ca2+ channel 'activator', dramatically enhanced the entry of Ca2+ and the secretory response in depolarized cells. 7. In voltage-clamped cells, switching the holding potential from -80 to -40 mV promoted the loss of 80 % of the whole-cell inward Ca2+ channel current carried by 10 mM Ba2+ (IBa). The residual current was blocked by 80 % upon addition of 3 microM nifedipine and dramatically enhanced by 3 microM FPL64176. 8. Thus, it seems that the N- and P/Q-subtypes of calcium channels are more prone to inactivation at depolarizing voltages than the L-subtype. We propose that this different inactivation might occur physiologically during different patterns of action potential firing, triggered by endogenously released acetylcholine under various stressful conditions.

Unmasking the functions of the chromaffin cell alpha7 nicotinic receptor by using short pulses of acetylcholine and selective blockers

Methyllycaconitine (MLA), alpha-conotoxin ImI, and alpha-bungarotoxin inhibited the release of catecholamines triggered by brief pulses of acetylcholine (ACh) (100 microM, 5 s) applied to fast-superfused bovine adrenal chromaffin cells, with IC50s of 100 nM for MLA and 300 nM for alpha-conotoxin ImI and alpha-bungarotoxin. MLA (100 nM), alpha-conotoxin ImI (1 microM), and alpha-bungarotoxin (1 microM) halved the entry of 45Ca2+ stimulated by 5-s pulses of 300 microM ACh applied to incubated cells. These supramaximal concentrations of alpha7 nicotinic receptor blockers depressed by 30% (MLA), 25% (alpha-bungarotoxin), and 50% (alpha-conotoxin ImI) the inward current generated by 1-s pulses of 100 microM ACh, applied to voltage-clamped chromaffin cells. In Xenopus oocytes expressing rat brain alpha7 neuronal nicotinic receptor for acetylcholine nAChR, the current generated by 1-s pulses of ACh was blocked by MLA, alpha-conotoxin ImI, and alpha-bungarotoxin with IC50s of 0.1 nM, 100 nM, and 1.6 nM, respectively; the current through alpha3 beta4 nAChR was unaffected by alpha-conotoxin ImI and alpha-bungarotoxin, and weakly blocked by MLA (IC50 = 1 microM). The functions of controlling the electrical activity, the entry of Ca2+, and the ensuing exocytotic response of chromaffin cells were until now exclusively attributed to alpha3 beta4 nAChR; the present results constitute the first evidence to support a prominent role of alpha7 nAChR in controlling such functions, specially under the more physiological conditions used here to stimulate chromaffin cells with brief pulses of ACh.

Synergism between toxin-gamma from Brazilian scorpion Tityus serrulatus and veratridine in chromaffin cells

Toxin-gamma (Tgamma) from the Brazilian scorpion Tityus serrulatus venom caused a concentration- and time-dependent increase in the release of norepinephrine and epinephrine from bovine adrenal medullary chromaffin cells. Tgamma was approximately 200-fold more potent than veratridine judged from EC50 values, although the maximal secretory efficacy of veratridine was 10-fold greater than that of Tgamma (1.2 vs. 12 microg/ml of catecholamine release). The combination of both toxins produced a synergistic effect that was particularly drastic at 5 mM extracellular Ca2+ concentration ([Ca2+]o), when 30 microM veratridine plus 0.45 microM Tgamma were used. Tgamma (0.45 microM) doubled the basal uptake of 45Ca2+, whereas veratridine (100 microM) tripled it. Again, a drastic synergism in enhancing Ca2+ entry was seen when Tgamma and veratridine were combined; this was particularly pronounced at 5 mM [Ca2+]o. Veratridine induced oscillations of cytosolic Ca2+ concentration ([Ca2+]i) in single fura 2-loaded cells without elevation of basal levels. In contrast, Tgamma elevated basal [Ca2+]i levels, causing only small oscillations. When added together, Tgamma and veratridine elevated the basal levels of [Ca2+]i without causing large oscillations. Tgamma shifted the current-voltage (I-V) curve for Na+ channel current to the left. The combination of Tgamma with veratridine increased the shift of the I-V curve to the left, resulting in a greater recruitment of Na+ channels at more hyperpolarizing potentials. This led to enhanced and more rapid accumulation of Na+ in the cell, causing cell depolarization, the opening of voltage-dependent Ca2+ channels, and Ca2+ entry and secretion.

Stationary phase induction of dnaN and recF, two genes of Escherichia coli involved in DNA replication and repair

The beta subunit of DNA polymerase III holoenzyme, the Escherichia coli chromosomal replicase, is a sliding DNA clamp responsible for tethering the polymerase to DNA and endowing it with high processivity. The gene encoding beta, dnaN, maps between dnaA and recF, which are involved in initiation of DNA replication at oriC and resumption of DNA replication at disrupted replication forks, respectively. In exponentially growing cells, dnaN and recF are expressed predominantly from the dnaA promoters. However, we have found that stationary phase induction of the dnaN promoters drastically changes the expression pattern of the dnaA operon genes. As a striking consequence, synthesis of the beta subunit and RecF protein increases when cell metabolism is slowing down. Such an induction is dependent on the stationary phase sigma factor, RpoS, although the accumulation of this factor alone is not sufficient to activate the dnaN promoters. These promoters are located in DNA regions without static bending, and the -35 hexamer element is essential for their RpoS-dependent induction. Our results suggest that stationary phase-dependent mechanisms have evolved in order to coordinate expression of dnaN and recF independently of the dnaA regulatory region. These mechanisms might be part of a developmental programme aimed at maintaining DNA integrity under stress conditions.

Analogies and differences between omega-conotoxins MVIIC and MVIID: binding sites and functions in bovine chromaffin cells

The characteristics of the binding sites for the Conus magus toxins omega-conotoxin MVIIC and omega-conotoxin MVIID, as well as their effects on K+-evoked 45Ca2+ entry and whole-cell Ba2+ currents (IBa), and K+-evoked catecholamine secretion have been studied in bovine adrenal chromaffin cells. Binding of [125I] omega-conotoxin GVIA to bovine adrenal medullary membranes was displaced by omega-conotoxins GVIA, MVIIC and MVIID with IC50 values of around 0.1, 4 and 100 nM, respectively. The reverse was true for the binding of [125I] omega-conotoxin MVIIC, which was displaced by omega-conotoxins MVIIC, MVIID and GVIA with IC50 values of around 30, 80 and 1.200 nM, respectively. The sites recognized by omega-conotoxins MVIIC and MVIID in bovine brain exhibited higher affinities (IC50 values of around 1 nM). Both omega-conotoxin MVIIC and MVIID blocked IBa by 70-80%; the higher the [Ba2+]o of the extracellular solution the lower the blockade induced by omega-conotoxin MVIIC. This was not the case for omega-conotoxin MVIID; high Ba2+ (10 mM) slowed down the development of blockade but the maximum blockade achieved was similar to that obtained in 2 mM Ba2+. A further difference between the two toxins concerns their reversibility; washout of omega-conotoxin MVIIC did not reverse the blockade of IBa while in the case of omega-conotoxin MVIID a partial, quick recovery of current was produced. This component was irreversibly blocked by omega-conotoxin GVIA, suggesting that it is associated with N-type Ca2+ channels. Blockade of K+-evoked 45Ca2+ entry produced results which paralleled those obtained by measuring IBa. Thus, 1 microM of each of omega-conotoxin GVIA and MVIIA inhibited Ca2+ uptake by 25%, while 1 microM of each of omega-conotoxin MVIIC and MVIID caused a 70% blockade. K+-evoked catecholamine secretory responses were not reduced by omega-conotoxin GVIA (1 microM). In contrast, at 1 microM both omega-conotoxin MVIIC and MVIID reduced the exocytotic response by 70%. These data strengthen the previously established conclusion that Q-type Ca2+ channels that contribute to the regulation of secretion and are sensitive to omega-conotoxins MVIIC and MVIID are present in bovine chromaffin cells. These channels, however, seem to possess binding sites for omega-conotoxins MVIIC and MVIID whose characteristics differ considerably from those described to occur in the brain; they might represent a subset of Q-type Ca2+ channels or an entirely new subtype of voltage-dependent high-threshold Ca2+ channel.

Differential effects of forskolin and 1,9-dideoxy-forskolin on nicotinic receptor- and K+-induced responses in chromaffin cells

The diterpene forskolin inhibits nicotine-evoked chromaffin cell Ca2+ influx, scinderin redistribution, F-actin disassembly and catecholamine secretion in a concentration-dependent (10-50 microM) fashion. On the other hand, forskolin showed weak inhibitory effects when the same responses were elicited by K+-induced depolarization. Similar concentrations of 1,9-dideoxy-forskolin, a forskolin analog which does not activate adenylate cyclase, blocked very effectively the responses evoked by either of the two stimuli. Patch-clamp (whole-cell configuration) studies demonstrated that both diterpenes blocked fast and reversibly peak and total chromaffin cell nicotinic acetylcholine receptor currents, effects not mediated through adenylate cyclase activation. Moreover, both forskolin and 1,9-dideoxy-forskolin exhibited Ca2+ channel blocking properties. However, 1,9-dideoxy-forskolin was more potent than forskolin as a Ca2+ channel blocker. Furthermore, 1,9-dideoxy-forskolin was also more potent than forskolin as a nicotinic acetylcholine receptor and Ca2+ channel blocker and it was more potent as a nicotinic acetylcholine receptor blocker than Ca2+ channel blocker. The results showed powerful cAMP-independent effects of the diterpenes and suggest caution in interpretation of cAMP effects on chromaffin cells when its cellular levels are modified by forskolin.

A caffeine-sensitive Ca2+ store modulates K+-evoked secretion in chromaffin cells

Catecholamine release from bovine adrenal medulla chromaffin cells superfused with a Krebs-N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid solution was monitored on-line with an electrochemical detector. Caffeine (10 mM) progressively depressed the magnitude of secretory responses to depolarizing pulses of 70 mM K+ and 2 mM Ca2+ (70 K+/2 Ca2+) in cells superfused with a Krebs-N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid solution containing 0 mM Ca2+ + 0.5 mM EGTA; blockade reached 80% at the third 70 K+/2 Ca2+ challenge given in the presence of caffeine. A similar effect was obtained when, instead of continuous superfusion, prepulses of caffeine were applied (10 mM for 60 s). The blocking effects of caffeine on K+-induced secretion depended on the time of exposure to the drug: the longer the exposure time the greater the blockade. The recovery of the K+ secretory responses previously impaired by caffeine was always gradual and followed a staircase mode. This contrasts with the effects of caffeine on various parameters measuring Ca2+ entry through Ca2+ channels, which did not parallel its effects on K+-evoked secretion. The secretion data, however, are compatible with the disappearance and recovery of an intracellular Ca2+ concentration signal triggered by K+ in single chromaffin cells loaded with fura 2 and treated with 10 mM caffeine. Thus, contrary to previous views, the depression of secretion by caffeine does not seem to be associated with inhibition of extracellular Ca2+ entry through Ca2+ channels. These functional data are, rather, compatible with the view that the degree of filling of a caffeine-sensitive intracellular Ca2+ store might regulate the extent of exocytosis. When emptied, such a store might act as a sink for the external Ca2+ entering through Ca2+ channels during cell depolarization, thus decreasing the intracellular Ca2+ concentration available for exocytosis.

Distinct effects of omega-toxins and various groups of Ca(2+)-entry inhibitors on nicotinic acetylcholine receptor and Ca2+ channels of chromaffin cells

The effects of omega-toxins and various Ca2+ antagonist subtypes on the 45Ca2+ entry into bovine adrenal medullary chromaffin cells stimulated via nicotinic acetylcholine receptors or via direct depolarization with K+, have been compared. The conditions selected to stimulate the 45Ca2+ entry consisted of a 60-s period of exposure of cells to 100 microM of the nicotinic acetylcholine receptor agonist dimethylphenylpiperazinium or to 70 mM K+. The N-type voltage-dependent Ca2+ channel blockers omega-conotoxin GVIA and MVIIA (1 microM) inhibited 45Ca2+ entry stimulated by dimethylphenylpiperazinium or K+ by around 25-30%. The P-type Ca2+ channel blocker omega-agatoxin IVA (10 nM) did not affect the dimethylphenylpiperazinium nor the K+ responses; 1 microM (Q-channel blockade) inhibited both responses by around 50%. The N/P/Q-type Ca2+ channel blocker omega-contoxin MVIIC (1 microM) inhibited the K+ evoked 45Ca2+ entry by 70%, while dimethylphenylpiperazinium was blocked by 50% (P < 0.001). The L-type Ca2+ channel blockers nifedipine, furnidipine, diltiazem or verapamil (3 microM each) inhibited much more the dimethylphenylpiperazinium than the K+ response. The dimethylphenylpiperazinium signal was blocked 71, 88, 89, and 53%, respectively, by nifedipine, furnidipine, diltiazem and verapamil, and the K+ response by 38, 29, 22, and 10%. Combined omega-conotoxin MVIIC (1 microM) and furnidipine (3 microM) blocked 100% of the K+ evoked 45Ca2+ entry. However, combined omega-conotoxin GVIA (1 microM), and furnidipine left unblocked 50% of the K+ response. The "wide spectrum' Ca2+ channel antagonists flunarizine or dotarizine (3 microM each) blocked the dimethylphenylpiperazinium and the K+ responses to a similar extent (50%); cinnarizine (3 microM) inhibited more the dimethylphenylpiperazinium (82%) than the K+ response (21%). At 3 microM, the highly lipophilic beta-adrenoceptor antagonist (+/-)-propranolol, reduced by 68% the dimethylphenylpiperazinium signal and by 23% the K+ signal. Other high lipophilic beta-adrenoceptor antagonists such as metoprolol and labetalol, reduced little the dimethylphenylpiperazinium and the K+ responses. The highly lipophilic agent penfluridol blocked the dimethylpiperazinium response by 30% and the K+ response by 50%. One of the least lipophilic compounds tested, (+)-lubeluzole, blocked by 40% the dimethylphenylpiperazinium and the K+ responses. These data are compatible with the idea that the various omega-toxin peptides used to separate pharmacologically the different voltage-dependent Ca2+ channels expressed by neurones, do not block the neuronal nicotinic acetylcholine receptor ion channel. In contrast the L-type Ca2+ channel blockers do block the nicotinic acetylcholine receptor ionophore. Lipophilicity of the compounds is not a requirement for Ca2+ channel or nicotinic acetylcholine receptor blockade.

Synthesis and pharmacology of alkanediguanidinium compounds that block the neuronal nicotinic acetylcholine receptor

Taking as models the polyamine toxin fraction FTX from the funnel-web spider venom, and the guanidinium moiety of guanethidine, a series of azaalkane-1, omega-diguanidinium salts were obtained. Some of them blocked ion fluxes through the neuronal nicotinic receptors for acetylcholine (nAChR). The blockade was exerted at submicromolar concentrations, suggesting a highly selective interaction with the nAChR. In fact, the active compounds on the nAChR ion channel did not recognize the voltage-dependent Na+ or Ca2+ channels of bovine adrenal chromaffin cells. Therefore, these compounds may be useful tools to clarify the functions of nAChR receptors in the central and peripheral nervous systems.

Inhibition of nicotinic receptor-mediated responses in bovine chromaffin cells by diltiazem

1. The effects of diltiazem on various functional parameters were studied in bovine cultured adrenal chromaffin cells stimulated with the nicotinic receptor agonist dimethylphenylpiperazinium (DMPP) or with depolarizing Krebs-HEPES solutions containing high K+ concentrations. 2. The release of [3H]-noradrenaline induced by DMPP (100 microM for 5 min) was gradually and fully inhibited by increasing concentrations of diltiazem (IC50 = 1.3 microM). In contrast, the highest concentration of diltiazem used (10 microM) inhibited the response to high K+ (59 mM for 5 min) by only 25%. 3. 45Ca2+ uptake into cells stimulated with DMPP (100 microM for 1 min) was also blocked by diltiazem in a concentration-dependent manner (IC50 = 0.4 microM). Again, diltiazem blocked the K(+)-evoked 45Ca2+ uptake (70 mM K+ for 1 min) only by 20%. In contrast, the N-P-Q-type Ca2+ channel blocker omega-conotoxin MVIIC depressed the K+ signal by 70%. In the presence of this toxin, diltiazem exhibited an additional small inhibitory effect, indicating that the compound was acting on L-type Ca2+ channels. 4. Whole-cell Ba2+ currents through Ca2+ channels in voltage-clamped chromaffin cells were inhibited by 3-10 microM diltiazem by 20-25%. The inhibition was readily reversed upon washout of the drug. 5. The whole-cell currents elicited by 100 microM DMPP (IDMPP) were inhibited in a concentration-dependent and reversible manner by diltiazem. Maximal effects were found at 10 microM, which reduced the peak IDMPP by 70%. The area of each curve represented by total current (QDMPP) was reduced more than the peak current. At 10 microM, the inhibition amounted to 80%; the IC50 for QDMPP inhibition was 0.73 microM, a figure close to the IC50 for 45Ca2+ uptake (0.4 microM) and [3H]-noradrenaline release (1.3 microM). The blocking effects of diltiazem developed very quickly and did not exhibit use-dependence; thus the drug blocked the channel in its closed state. The blocking effects of 1 microM diltiazem on IDMPP were similar at different holding potentials (inhibition by around 30% at -100, -80 or -50 mV). Diltiazem did not affect the current flow through voltage-dependent Na+ channels. 6. These data are compatible with the idea that diltiazem has little effect on Ca2+ entry through voltage-dependent Ca2+ channels in bovine chromaffin cells. Neither, does diltiazem affect INa. Rather, diltiazem acts directly on the neuronal nicotinic receptor ion channel and blocks ion fluxes, cell depolarization and the subsequent Ca2+ entry and catecholamine release. This novel effect of diltiazem might have clinical relevance since it might reduce the sympathoadrenal drive to the heart and blood vessels, thus contributing to the well established antihypertensive and cardioprotective effects of the drug.

Blocking effects of otilonium on Ca2+ channels and secretion in rat chromaffin cells

We describe here the effects of otilonium bromide (an anticholinergic agent widely used as an intestinal spasmolytic) on whole-cell currents through Ca2+ channels (IBa) and catecholamine secretion in rat adrenal glands and isolated rat chromaffin cells. Otilonium blocked the peak IBa current in voltage-clamped chromaffin cells in a concentration-dependent manner; the IC50 to block IBa was 4.7 microM. Blockade was not accompanied by a significant shift in the I-V relationship for IBa, suggesting that such blockade was not affecting a specific subtype of Ca2+ channel. When given intracellularly through the patch pipette, otilonium (10 microM) did not block IBa. However, its external application to the same cell (10 microM) reversibly reduced IBa by 70%. Otilonium caused a concentration-dependent blockade of catecholamine release from perfused rat adrenal glands intermittently stimulated with methacholine, high K+ or histamine. The IC50 to block secretion after a 5 min incubation with otilonium was 0.02, 0.7 and 3 microM, respectively, for methacholine, K+ and histamine. The blocking effects of otilonium were fully reversible at concentrations below 10 microM. The Ca2+ channel agonist Bay K 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyr idine-5- carboxylate) partially antagonized the effects of otilonium on K(+)-evoked secretion and accelerated the time course of recovery from inhibition. The results are compatible with the idea that otilonium blocks Ca2+ entry into chromaffin cells by blocking voltage-dependent Ca2+ channels. This would lead to a limitation in the rise in cytosolic Ca2+ at secretory sites and to inhibition of catecholamine release in response to stimulation of chromaffin cells.

Otilonium: a potent blocker of neuronal nicotinic ACh receptors in bovine chromaffin cells

1. Otilonium, a clinically useful spasmolytic, behaves as a potent blocker of neuronal nicotinic acetylcholine receptors (AChR) as well as a mild wide-spectrum Ca2+ channel blocker in bovine adrenal chromaffin cells. 2. 45Ca2+ uptake into chromaffin cells stimulated with high K+ (70 mM, 1 min) was blocked by otilonium with an IC50 of 7.6 microM. The drug inhibited the 45Ca2+ uptake stimulated by the nicotinic AChR agonist, dimethylphenylpiperazinium (DMPP) with a 79 fold higher potency (IC50 = 0.096 microM). 3. Whole-cell Ba2+ currents (IBa) through Ca2+ channels of voltage-clamped chromaffin cells were blocked by otilonium with an IC50 of 6.4 microM, very close to that of K(+)-evoked 45Ca2+ uptake. Blockade developed in 10-20 s, almost as a single step and was rapidly and almost fully reversible. 4. Whole-cell nicotinic AChR-mediated currents (250 ms pulses of 100 microM DMPP) applied at 30 s intervals were blocked by otilonium in a concentration-dependent manner, showing an IC50 of 0.36 microM. Blockade was induced in a step-wise manner. Wash out of otilonium allowed a slow recovery of the current, also in discrete steps. 5. In experiments with recordings in the same cells of whole-cell IDMPP, Na+ currents (INa) and Ca2+ currents (ICa), 1 microM otilonium blocked 87% IDMPP, 7% INa and 13% ICa. 6. Otilonium inhibited the K(+)-evoked catecholamine secretory response of superfused bovine chromaffin cells with an IC50 of 10 microM, very close to the IC50 for blockade of K(+)-induced 45Ca2+ uptake and IBa. 7. Otilonium inhibited the secretory responses induced by 10 s pulses of 50 microM DMPP with an IC50 of 7.4 nM. Hexamethonium blocked the DMPP-evoked responses with an IC50 of 29.8 microM, 4,000 fold higher than that of otilonium. 8. In conclusion, otilonium is a potent blocker of nicotinic AChR-mediated responses. The drugs also blocked various subtypes of neuronal voltage-dependent Ca2+ channels at a considerably lower potency. Na+ channels were unaffected by otilonium. This extraordinary potency of otilonium in blocking nicotinic AChR, unrecognised until now, might account in part for its well known spasmolytic effects.

Dotarizine versus flunarizine as calcium antagonists in chromaffin cells

1. Dotarizine is a novel piperazine derivative structurally related to flunarizine that is currently being evaluated in clinical trials for its antimigraine and antivertigo effects. This clinical profile may be related to its Ca2+ antagonist properties. Therefore, the actions of both compounds as calcium antagonists were compared in bovine chromaffin cells. 2. Dotarizine and flunarizine blocked 45Ca2+ uptake into K+ depolarized chromaffin cells (70 mM K+/0.5 mM Ca2+ for 60 s) in a concentration-dependent manner, with IC50s of 4.8 and 6.7 microM, respectively. 3. Dotarizine and flunarizine also inhibited the whole-cell Ca2+ and Ba2+ currents (ICa, IBa) in voltage-clamped chromaffin cells, induced by depolarizing test pulses to 0 mV, during 50 ms, from a holding potential of -80 mV. Blockade exhibited IC50s of 4 microM for dotarizine and 2.2 microM for flunarizine. Dotarizine increased the rate of inactivation of ICa and IBa; inhibition of whole-cell currents was use-dependent. 4. Transient increases of the cytosolic Ca2+ concentration, [Ca2+]i, produced by K+ stimulation (70 mM K+ for 5 s) of single fura-2-loaded chromaffin cells, were also inhibited by dotarizine and flunarizine with IC50s of 1.2 and 0.6 microM, respectively. Upon washout of dotarizine, the [Ca2+]i increases recovered fully after 5-10 min. In contrast, the responses remained largely inhibited 10 min after washing out flunarizine. 5. Catecholamine release induced by K+ stimulation (10-s pulses of 70 mM) was inhibited by dotarizine with an IC50 of 2.6 microM and by flunarizine with an IC50 of 1.2 microM. The blocking effects of both compounds developed slowly, and was fully established after 20-30 min of superfusion. While blockade by dotarizine quickly reversed upon its washout, that of flunarizine lasted even 25 min after washing out.6. Catecholamine release from electroporated chromaffin cells triggered by 10 micro M Ca2+ was not affected by 10 micro M dotarizine or flunarizine.7. Overall, the results suggest that dotarizine behaves as a Ca2+ antagonist in bovine chromaffin cells. It exhibits a potency similar to flunarizine in blocking Ca2+ entry, Ca2+ channels, Cai2+ signals and secretion. The dotarizine effects are readily reversible suggesting that in contrast to flunarizine, it does not accumulate in cells. Dotarizine is devoid of intracellular effects on the secretory machinery. All its blocking effects on Ca2+ entry, [Ca2+]i rise and secretion are probably due to blockade of various Ca2+channel subtypes in chromaffin cells. This blockade is use-dependent and seems to be due to the increase by dotarizine of the rate of Ca2+ channel inactivation.

Q- and L-type Ca2+ channels dominate the control of secretion in bovine chromaffin cells

Potassium-stimulated catecholamine release from superfused bovine adrenal chromaffin cells (70 mM K+ in the presence of 2 mM Ca2+ for 10 s, applied at 5-min intervals) was inhibited by the dihydropyridine furnidipine (3 microM) by 50%. omega-Conotoxin MVIIC (CTx-MVIIC, 3 microM) also reduced the secretory response by about half. Combined CTx-MVIIC plus furnidipine blocked 100% catecholamine release. 45Ca2+ uptake and cytosolic Ca2+ concentrations ([Ca2+]i) in K(+)-depolarized cells were partially blocked by furnidipine or CTx-MVIIC, and completely inhibited by both agents. The whole cell current through Ca2+ channels carried by Ba2+ (IBa) was partially blocked by CTx-MVIIC. Although omega-conotoxin GVIA (CTx-GVIA, 1 microM) and omega-agatoxin IVA (Aga-IVA, 0.2 microM) partially inhibited 45Ca2+ entry, IBa and the increase in [Ca2+]i, the combination of both toxins did not affect the K(+)-evoked secretory response. The results are compatible with the presence in bovine chromaffin cells of a Q-like Ca2+ channel which has a prominent role in controlling exocytosis. They also suggest that Q- and L-type Ca2+ channels, but not N- or P-types are localized near exocytotic active sites in the plasmalemma.

Endothelium-independent relaxation by 17-alpha-estradiol of pig coronary arteries

We have studied the effects of 17-alpha-estradiol, a non-estrogenic steroid, on pig coronary arteries contracted by K+, Ca2+ or serotonin. Experiments were performed on helicoidal strips and rings of left circumflex coronary arteries from freshly slaughtered white pigs and on helicoidal strips of rat thoracic aorta. The strips and rings were suspended inside a water-jacketed muscle chamber in an oxygenated Krebs solution at 37 degrees C. From the initial K(+)-evoked contraction, 17-alpha-estradiol caused a relaxation with an IC50 (15 microM) which was in the range of the IC50s obtained for nitroglycerin (1.3 microM) and nicorandil (50 microM). Contractions evoked by Ca2+ were inhibited by 17-alpha-estradiol, but full blockade could not be achieved. Serotonin-evoked contractions were also blocked by 17-alpha-estradiol with an IC50 of 2.1 microM; 17-beta-estradiol also inhibited the serotonin-evoked contractions. In the presence of 100 microM of the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester, the relaxing properties of 17-alpha-estradiol in pig coronary arteries and rat thoracic aorta were unaffected, suggesting that endothelial NO release was unrelated to these effects. 17-alpha-Estradiol also relaxed denuded pig coronary artery strips, suggesting that other endothelial-derived relaxing factors were not involved in its vascular effects. The results are compatible with the idea that 17-alpha-estradiol causes relaxation of coronary vessels by acting directly on the cell membrane of smooth muscle cells; these effects seem to be unrelated to the genomic physiological effects of estrogens.(ABSTRACT TRUNCATED AT 250 WORDS)

The nicotinic acetylcholine receptor of the bovine chromaffin cell, a new target for dihydropyridines

The effects of 1,4-dihydropyridine derivatives on divalent cation transients and catecholamine release stimulated by either high K+ or the nicotinic receptor agonist dimethyl-phenyl-piperazinium (DMPP) have been compared in bovine adrenal chromaffin cells. The activation of Ca2+ entry pathways was followed by measuring 45Ca2+ or Mn2+ uptake, or by the changes of [Ca2+]i in fura-2-loaded chromaffin cells. Various dihydropyridine Ca2+ channel blockers (nimodipine, PCA50938, nifedipine, nitrendipine, furnidipine) abolished the DMPP-mediated effects, but prevented only partially the activation by high [K+]0 of 45Ca2+ uptake. The IC50 for DMPP-induced activation was around 1 microM. The L-type Ca2+ channel activator Bay K 8644 potentiated the uptake of 45Ca2+ induced by K+ depolarization at concentrations between 10 nM and 1 microM, but completely inhibited the uptake of 45Ca2+ by DMPP (IC50, 0.9 microM). Both high [K+]0 and DMPP produced membrane depolarization as measured using bis-oxonol. The DMPP-evoked, but not the K(+)-evoked membrane depolarization was prevented by Na+ removal, suggesting that the depolarization was due to Na+ entry through the acetylcholine receptor ionophore. Nimodipine at 10 microM abolished the depolarization induced by DMPP, leaving the K(+)-evoked depolarization unaffected. Tetrodotoxin (2 microM) did not affect the DMPP- or high K(+)-mediated cell depolarization. Whole-cell inward current evoked by 100 microM DMPP (IDMPP) was measured in cells voltage-clamped at -80 mV. Nimodipine (10 microM) reduced IDMPP by 36%; Bay K 8644 (10 microM) inhibited IDMPP by 67%. DMPP-evoked catecholamine release from superfused chromaffin cells was reduced by over 90% with 10 microM nimodipine; in contrast, K(+)-evoked release was decreased by 20%.(ABSTRACT TRUNCATED AT 250 WORDS)

PCA 50941, a novel Ca2+ channel agonist

PCA 50941 is a novel 1,4-dihydropyridine derivative. Its vasoconstricting effects prompted a systematic comparison with the prototypic Ca2+ channel activator, Bay K 8644. The two compounds exhibit marked analogies and differences in their cardiovascular profiles. PCA 50941 exhibits a pronounced vascular over cardiac selectivity while Bay K 8644 has both potent vasoconstrictor effects and strong cardiac positive inotropic actions. PCA 50941 exhibits either poor positive inotropic effects (isolated guinea-pig atria) or clear negative inotropic effects (isolated perfused rat heart). Both compounds reduced by 10-40% the coronary flow in the perfused rat heart. However, PCA 50941 had slight vasoconstrictor effects in pig coronary arteries, causing their relaxation at nanomolar/micromolar concentrations; this contrasts with the almost pure, marked vasoconstrictor effects of Bay K 8644 in coronary arteries. In the rat aorta PCA 50941 exhibited a biphasic pattern of vasoconstriction and vasorelaxation, and in portal vein it markedly reduced the Ca(2+)-evoked contractions; Bay K 8644 behaved as a pure vasoconstrictor in these two preparations. It is concluded that the racemic compound, PCA 50941, exhibits different degrees of Ca2+ agonism and Ca2+ antagonism by acting upon 1,4-dihydropyridine receptors of different cardiovascular tissues. Its tissue selectivity and its prolonged duration of action give PCA 50941 a cardiovascular profile more favourable than that of other 1,4-dihydropyridine Ca2+ agonist existing to date.

Synthesis of 3-[(2,3-dihydro-1,1,3-trioxo-1,2-benzisothiazol-2-yl)alkyl] 1,4-dihydropyridine-3,5-dicarboxylate derivatives as calcium channel modulators

1,4-Dihydropyridine (DHP) derivatives with a 1,2-benzisothiazol-3-one 1,1-dioxide group, linked through an alkylene bridge to the C-3 carboxylate of the DHP ring, with both vasoconstricting and vasorelaxant properties were obtained. In blocking Ca(2+)-evoked contractions of K(+)-depolarized rabbit aortic strips, compounds 12 and 41 were 10-fold more potent than nifedipine; 27 other compounds were 1-4-fold more potent. Their vascular versus cardiac selectivity was very pronounced; for instance, the selectivity index for compound 41 was 70-fold higher than that of nifedipine. This was also true for the vasoconstricting compound 22, which was as potent as Bay K 8644 in enhancing the Ca(2+)-evoked contractions of rabbit aorta strips, yet it had poor inotropic activity in rabbit left atria. Oral administration of compounds 38, 40, 43, and 53 (20 mg/kg) caused a 35-37% decrease in systolic blood pressure in spontaneously hypertensive rats (SHR); these effects were similar to those of nifedipine. However, iv administration of these compounds to anesthetized SHR caused a decrease in blood pressure which was more pronounced and long-lasting than that of nifedipine. When administered iv at 100 micrograms/kg, the vasoconstricting compound 22 caused a 40% increase in systolic and diastolic blood pressure. Compound 22 exhibited an unusually interesting feature over the other five Ca2+ DHP agonists: it had diester substitutions at the C-3 and C-5 positions of the DHP ring. Overall, compounds possessing these properties might be useful in treating clinical cardiovascular conditions in which DHP Ca2+ antagonists or agonists are indicated.

4-Alkyl-1,4-dihydropyridines derivatives as specific PAF-acether antagonists

A new series of 4-alkyl-1,4-dihydropyridines (1,4-DHP) were synthesized and evaluated for their ability to inhibit washed rabbit platelet aggregation induced by PAF-acether (1-O-hexadecyl/octadecyl-2-O-acetyl-sn-glycero-3-phosphorylcholine) and to reverse PAF-induced hypotension in anesthetized rats. Additionally, compounds were evaluated for their ability to inhibit the binding of radiolabeled PAF to its receptor on rabbit platelets. Among these compounds, 6I and 6L were the most potent and specific antagonists. At concentrations up to 100 microM, neither compound 6I nor compound 6L caused platelet aggregation nor did they inhibit platelet aggregation induced by collagen or adenosine diphosphate. Compound 6L did not show in vitro calcium channel blocker activity measured on vascular smooth muscle preparations of rabbit aorta and on [3H]nitrendipine binding assays. The compound did not show any cardiovascular effects in anesthetized rat at iv doses up to 1000 micrograms/kg, and the Ki value was 568.62 nmol. These results indicate that compound 6L is a potent and specific PAF antagonist with 1,4-dihydropyridine structure but devoid of a significant cardiovascular activity related to calcium-antagonist properties.