piperidines and 4-desmethoxyverapamil

Topics: Albuterol; Animals; Binding, Competitive; Calcium Channels; Capsaicin; Dose-Response Relationship, Drug; Guinea Pigs; Kinetics; Lung; Neurokinin A; Neurokinin-1 Receptor Antagonists; Piperidines; Receptors, Neurokinin-1; Thiorphan; Verapamil

The L-type Ca2+ channel is blocked by 1,4-dihydropyridines (DHP), by phenylalkylamines, by diphenylbutylpiperidines or by benzolactams. We first show with mouse muscle cells in culture that all these L-type Ca2+ channel blockers block contraction. However, voltage-clamp analysis associated to contraction measurements also clearly show that Ca2+ influx through L-type Ca2+ channels is not required for contraction. Therefore, there is a need for a voltage-sensor which would be responsible for the excitation-contraction (E-C) coupling. We are showing here that the voltage-sensor involved in E-C coupling and the L-type Ca2+ channel have a similar pharmacology. Some of the blockers used are more active on the voltage sensor, others on the L-type Ca2+ channel.

Topics: Action Potentials; Animals; Calcium Channel Blockers; Calcium Channels; Cells, Cultured; Dihydropyridines; Evoked Potentials; Isradipine; Mice; Muscle Contraction; Oxadiazoles; Piperidines; Thiazines; Verapamil

Benzolactams (HOE 166 and analogs) form a new class of molecules acting on the 1,4-dihydropyridine-sensitive L-type Ca2+ channels. The main binding properties of HOE 166 and analogs to rabbit skeletal muscle membranes are as follows. (i) The compounds have a specific binding site to which they associate with a high affinity (0.25 nM for HOE 166). (ii) Unlabeled HOE 166 and analogs completely inhibit 1,4-dihydropyridine binding [(+)-[3H]PN 200-110] in a competitive way. (iii) Affinity values measured for HOE 166 inhibition of (+)-[3H]PN 200-110 (K0.5 = 0.25 nM and K1 = 0.55 nM) and of [3H]HOE 166 binding (K0.5 = 0.5 nM) are in good agreement. They also fit with results from direct binding experiments with tritiated HOE 166 (Kd = 0.27 nM) and from kinetic experiments (Kd = 0.39 nM). (iv) HOE 166 completely inhibits the specific binding of other classes of Ca2+ channel antagonists such as phenylalkylamines [(-)[3H] desmethoxyverapamil], benzothiazepines (d-cis-[3H]diltiazem), diphenylbutylpiperidines ([3H]fluspirilene), and [3H]bepridil. In all these cases the binding inhibition is of a noncompetitive nature. (v) The maximum binding capacity for [3H]HOE 166 binding to transverse tubule membranes, 65 pmol/mg of protein, is the same as that found for other classes of Ca2+ channel antagonists. 45Ca2+ uptake experiments performed with the rat aortic cell line A7r5 and the insulin-secreting cell line RINm5F demonstrate that HOE 166 and analogs fully inhibit the 1,4-dihydropyridine-sensitive 45Ca2+ influx elicited by depolarization. There is a good correlation between inhibitory potencies of compounds in the HOE 166 series measured on (+)-[3H]PN 200-110 binding to A7r5 membranes and on the activity of Ca2+ channels followed by 45Ca2+ fluxes with the same cells. Structure-function relationships of HOE 166 and analogs for Ca2+ channel blockade in A7r5 and RINm5F cells were also in good correlation. Finally, voltage-clamp experiments confirmed that voltage-dependent L-type Ca2+ channels are completely blocked by 100 nM HOE 166 even at a membrane potential held at -80 mV.

Topics: Animals; Bepridil; Binding Sites; Calcium Channel Blockers; Cell Line; Dihydropyridines; Fluspirilene; Isradipine; Kinetics; Muscles; Oxadiazoles; Piperidines; Pyrrolidines; Rabbits; Rats; Structure-Activity Relationship; Thiazines; Verapamil