snx-230 and furnidipine

Rat alpha3beta4 or alpha7 neuronal nicotinic acetylcholine receptors (AChRs) were expressed in Xenopus laevis oocytes, and the effects of various toxins and non-toxin Ca2+ channel blockers studied. Nicotinic AChR currents were elicited by 1 s pulses of dimethylphenylpiperazinium (DMPP, 100 microM) applied at regular intervals. The N/P/Q-type Ca2+ channel blocker omega-conotoxin MVIIC inhibited alpha3beta4 currents with an IC50 of 1.3 microM; the blockade was non-competitive and reversible. The alpha7 currents were unaffected. At 1 microM, omega-conotoxin GVIA (N-type Ca2+ channel blocker) inhibited by 24 and 20% alpha3beta4 and alpha7 currents, respectively. At 1 microM, omega-agatoxin IVA (a P/Q-type Ca2+ channel blocker) did not affect alpha7 currents and inhibited alpha3beta4 currents by only 15%. L-type Ca2+ channel blockers furnidipine, verapamil and, particularly, diltiazem exhibited a preferential blocking activity on alpha3beta4 nicotinic AChRs. The mechanism of alpha3beta4 currents blockade by omega-conotoxins and diltiazem differed in the following aspects: (i) the onset and reversal of the blockade was faster for toxins; (ii) the blockade by the peptides was voltage-dependent, while that exerted by diltiazem was not; (iii) diltiazem promoted the inactivation of the current while omega-toxins did not. These data show that, at concentrations currently employed as Ca2+ channel blockers, some of these compounds also inhibit certain subtypes of nicotinic AChR currents. Our data calls for caution when interpreting many of the results obtained in neurons and other cell types, where nicotinic receptor and Ca2+ channels coexist.

Topics: Animals; Calcium Channel Blockers; Dihydropyridines; Diltiazem; Dimethylphenylpiperazinium Iodide; Electric Stimulation; Female; Kinetics; Membrane Potentials; Neurons; Nicotinic Agonists; omega-Conotoxin GVIA; omega-Conotoxins; Oocytes; Peptides; Rats; Receptors, Nicotinic; Time Factors; Verapamil; Xenopus laevis

External Ca(2+) entry through various Ca(2+)-channel subtypes is responsible for the large oscillations of the cytosolic Ca(2+) concentrations, [Ca(2+)](i), and cell death induced by veratridine in primary cultures of bovine chromaffin cells. Blockade by omega-conotoxin GVIA (GVIA) of N-type Ca(2+) channels, by omega-agatoxin IVA (IVA) of P-type Ca(2+) channels, or by furnidipine of L-type Ca(2+) channels did not afford cytoprotection. However, (omega-conotoxin MVIIC (MVIIC), a wide-spectrum blocker of N-, P- and Q-type Ca(2+) channels greatly protected the cells against the cytotoxic effects of veratridine. Furnidipine further enhanced the cytoprotecting effects of MVIIC. MVIIC but not furuidipine, markedly reduced the oscillations of [Ca(2+)](i) induced by veratridine in single fura-2-loaded chromaffin cells. The results suggest that Ca(2+) entry through any of the different Ca(2+) channel subtypes present in bovine chromaffin cells might be cytotoxic. They also support two ideas: (i) that wide-spectrum neuronal Ca(2+) channel blockers (i.e. MVIIC) might be better cytoprotecting agents than more specific neuronal Ca(2+) channel blockers (i.e., GVIA, IVA, furnidipine); and (ii) that combined Ca(2+) channel blockers may provide greater cytoprotection than single compounds.

Topics: Adrenal Glands; Animals; Calcium; Calcium Channel Blockers; Catecholamines; Cattle; Chromaffin Cells; Dihydropyridines; Dose-Response Relationship, Drug; omega-Conotoxins; Peptides; Veratridine

By using the whole-cell configuration of the patch-clamp technique we have investigated the pharmacological properties of Ca2+ channels in short-term cultured rat chromaffin cells. In cells held at a membrane potential of --80 mV, using 10 mM Ba2+ as the charge carrier, only high-voltage-activated (HVA) Ca2+ channels were found. Ba2+ currents (IBa) showed variable sensitivity to dihydropyridine (DHP) Ca2+ channel agonists and antagonists. Furnidipine, a novel DHP antagonist, reversibly blocked the current amplitude by 22% and 48%, at 1 microM and 10 microM respectively, during short (15-50 ms) depolarizing pulses to 0 mV. The L-type Ca2+ channel agonist Bay K 8644 (1 microM) caused a variable potentiation of HVA currents that could be better appreciated at low rather than at high depolarizing steps. Increase of IBa was accompanied by a 20-mV shift in the activation curves for Ca2+ channels towards more hyperpolarizing potentials. Application of the conus toxin omega-conotoxin GVIA (GVIA; 1 microM) blocked 31% of IBa; blockade was irreversible upon removal of the toxin from the extracellular medium. omega-Agatoxin IVA (IVA; 100 nM) produced a 15% blockade of IBa. omega-Conotoxin MVIIC (MVIIC; 5 microM) produced a 36% blockade of IBa; such blockade seems to be related to both GVIA-sensitive (N-type) and GVIA-resistant Ca2+ channels. The sequential addition of supramaximal concentrations of furnidipine (10 microM), GVIA (1 microM), IVA (100 nM) and MVIIC (3 microM) produced partial inhibition of IBa, which were additive. Our data suggest that the whole cell IBa in rat chromaffin cells exhibits at least four components.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Adrenal Medulla; Animals; Barium; Calcium Channel Agonists; Calcium Channel Blockers; Calcium Channels; Catecholamines; Cells, Cultured; Dihydropyridines; Female; Ion Channel Gating; Ion Transport; Male; Membrane Potentials; omega-Agatoxin IVA; omega-Conotoxin GVIA; omega-Conotoxins; Patch-Clamp Techniques; Peptides; Rats; Species Specificity; Spider Venoms