Regulation of glycine uptake by calcium channel modulators in pulvinar cells of Mimosa pudica

Previous experiments have shown that calcium is involved in glycine uptake by pulvinar tissues of Mimosa pudica plants. Present data show that either inorganic (CdCl2) or organic calcium channels blockers from the dihydropyridine class (nifedipine, nisoldipine) and benzothiazepine class (diltiazem) reduced the glycine uptake whereas blockers from the phenylalkylamine class (verapamil and methoxyverapamil) did not significantly modify the process. By comparison, the calcium channel activator Bay K 8644 stimulated the amino acid absorption at low concentrations (10(-8)-10(-6) mol/L). Compounds known to affect the liberation of calcium from intracellular stores ( intracellular calcium modulators,,: TMB-8, cyclopiazonic acid, thapsigargin and LiCl) had no effect. Moreover, a clear correlation was noted between the action of the various calcium modulators on glycine absorption and on calcium uptake by me pulvinar tissues. Electrophysiological difference (Delta Psi), which is the electrical component of the proton motive force (PMF) energizing the glycine-H+ cotransport. Thus, the present data argue well for an involvement of calcium channels in the calcium-regulated uptake of a neutral amino acid and suggest that this Ca effect takes place at a specific step rather than by modifying the PMF.