REGULATION OF GLYCINE UPTAKE BY CALCIUM-CHANNEL MODULATORS IN PULVINAR CELLS OF MIMOSA-PUDICA

Previous experiments have shown that calcium is involved in glycine up take by pulvinar tissues of Mimosa pudica plants. Present data show th at either inorganic (CdCl2) or organic calcium channels blockers from the dihydropyridine class (nifedipine, nisoldipine) and benzothiazepin e class (diltiazem) reduced the glycine uptake whereas blockers from t he phenylalkylamine class (verapamil and methoxyverapamil) did not sig nificantly modify the process. By comparison, the calcium channel acti vator Bay K 8644 stimulated the amino acid absorption at low concentra tions (10(-8)-10(-6) mol/L). Compounds known to affect the liberation of calcium from intracellular stores ( intracellular calcium modulator s,,: TMB-8, cyclopiazonic acid, thapsigargin and LiCl) had no effect. Moreover, a clear correlation was noted between the action of the vari ous calcium modulators on glycine absorption and on calcium uptake by me pulvinar tissues. Electrophysiological difference (Delta Psi), whic h is the electrical component of the proton motive force (PMF) energiz ing 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.