Effects of Ultraviolet Radiation on Pinocytosis inAmoeba proteus

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Abstract
Ultraviolet (UV) irradiation (4000–10000 erg × mm‐2) decreased membrane potential and input resistance ofAmoeba proteusand induced formation of pinocytotic channels. Submaximal pinocytosis induced by UV light was additive to pinocytosis induced by K+or Na+and stimulated in the presence of EGTA. It was not inhibited by the presence of La+++or by pretreatment with dibucaine. In these respects and with respect to optimum pH and pCa, UV induced pinocytosis resembled potassium induced pinocytosis. Accumulation of K+in the amoeba membrane after a dose of radiation may explain the similarity between pinocytosis induced by UV light and potassium salts. Ca++present during the period of irradiation inhibited the effect of UV light. Instead Ca++applied after irradiation (1–20 mM) increased channel formation. This effect was stimulated by the presence of local anesthetic drugs. It is suggested that high doses of UV light may induce channel formation by releasing Ca++from the cell membrane into the cell (UV induced pinocytosis). Ca++may be released at the moment of absorption of UV light in the membrane as well as during the period of depolarization which follows irradiation. Low doses of UV light may permit extracellular Ca++to enter the cell and stimulate channel formation (calcium induced pinocytosis). Dithiotreitol (1 mM) applied after irradiation depressed both UV and calcium induced pinocytosis so these may be the result of the same structural change which involves the formation of disulphide bonds in the membrane.

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