Inhibition of Induced Pinocytosis in Amoeba proteus by Membrane Stabilizing Drugs

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Abstract
The effect of membrane stabilizing drugs on cation induced pinocytosis was studied inAmoeba 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>tetracaine> bupivacaine >lidocaine>procaine, and the phenothiazines: thioridazine>prochlorperazine>chlorpromazine > 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 × 10‐4M) 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.