title: Inhibition of induced pinocytosis in Amoeba proteus by membrane stabilizing drugs.
abstract: The effect of membrane stabilizing drugs on cation induced pinocytosis was studied in Amoeba proteus. Initially the presence of local anesthetic drugs during a pinocytosis cycle had a stimulating effect on channel formation, however, the capacity to develop pinocytotic channels was reversibly inhibited after a period of treatment with these drugs. Imipramine, vinblastine and the phenothiazines had effects similar to local anaesthetics. The local anesthetics inhibited pinocytosis in the following order: dibucaine greater than tetracaine greater than bupivacaine greater than lidocaine greater than procaine, and the phenothiazines: thioridazine greater than prochlorperazine greater chlorpromazine greater than prometazine. Pinocytosis, when induced by Na+ or tris, was more affected by the drugs and by calcium binding agents than pinocytosis induced by K+. After pretreatment with inhibitory concentration of dibucaine (3 x 10(-4) M) the depolarization of the membrane and the conductance increase during pinocytosis were normal, while the increase of oxygen uptake during the pincoytosis cycle was abolished. Addition of Ca++ before, during or after dibucaine treatment decreased the effect of the drug. Conversely, in dibucaine-treated cells, cation induced pinocytosis was less inhibited by Ca++ than pinocytosis in normal cells. Addition of EGTA to the inducing solutions potentiated the inhibitory effect of the drug. It is suggested that these drugs release Ca++ from the cell surface and at higher concentration or after prolonged incubation time interfere with a Ca++ mechanism which couples the membrane and contractile systems in the cytoplasm.
mesh_terms: D000656:Amoeba / Q000187:drug effects*; D000779:Anesthetics, Local / Q000494:pharmacology*; D014150:Antipsychotic Agents / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D003864:Depression, Chemical; D004347:Drug Interactions; D007099:Imipramine / Q000494:pharmacology*; D010640:Phenothiazines; D010873:Pinocytosis / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D014325:Tromethamine / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology*
chemical_list: D000779:Anesthetics, Local; D014150:Antipsychotic Agents; D010640:Phenothiazines; D014325:Tromethamine; D014747:Vinblastine; D012964:Sodium; D007099:Imipramine; D011188:Potassium; D002118:Calcium