Selective inhibition of calcium-stimulated cation-induced pinocytosis by starvation and inhibitors of protein synthesis in Amoeba proteus.
The capacity of Amoeba proteus to form pinocytotic channels after pretreatment with either puromycin, cycloheximide, emetine or a long period of starvation was studied. The effect on pinocytosis of the three inhibitors of protein synthesis was similar. They preferentially affected pinocytosis induced by Na+ with little effect on K+-induced pinocytosis. In Ca2+-deficient media, Na+-induced pinocytosis was inhibited, while the addition of Ca2+ restored channel formation. The degree of inhibition of Na+-induced pinocytosis was influenced by the concentration of Ca2+ in the inducing solution. Selective Ca2+-reversible inhibition of Na+-induced pinocytosis also occurred after starvation or treatment with a proteolytic enzyme, subtilisin. The membrane potential in starved or emetine-treated cells in culture medium was normal and their depolarising response to inducers was not diminished in solutions containing Na+. The resting input resistance of these cells was higher than in normal amoebae, but no significant difference in electrical parameters was observed after pinocytosis was induced. It is suggested that starvation, inhibition of protein synthesis, and enzyme digestion deplete the membrane of structures which are necessary for normal Ca2+ functions during induction of pinocytosis by Na+-like inducers.
D000656:Amoeba / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003470:Culture Media; D003513:Cycloheximide / Q000494:pharmacology; D004640:Emetine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D010873:Pinocytosis / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D014176:Protein Biosynthesis; D011691:Puromycin / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013381:Subtilisins / Q000494:pharmacology
D003470:Culture Media; D011691:Puromycin; D003513:Cycloheximide; D012964:Sodium; D013381:Subtilisins; D011188:Potassium; D002118:Calcium; D004640:Emetine