Retention of 14C-DDT in cellular fractions of vertebrate insecticide-resistant and susceptible fish

Abstract

DDT resistant and susceptible populations of mosquitofish ( Gambusia affinis) were assayed for DDT retention in particulate fractions of livers and brains following in vivo and in vitro treatment with 14C-DDT. Livers and brains were homogenized, and particulate fractions were prepared by differential centrifugation and counted for radioactivity. The in vivo studies indicate a significant difference in retention between brains from susceptible and resistant fish and point to a membrane barrier to DDT in tissues from resistant fish. There is also a more effective blood-brain barrier in resistant fish than in susceptible fish. There was a difference in total distribution of DDT based on percent retention in brain tissue of resistant and susceptible fish. It appears that the cell membranes of resistant fish retain DDT, thus reducing the amount entering the cell. The opposite effect is seen in the mitochondrial membrane as DDT is apparently prevented from entering rather than being membrane bound. In the in vivo liver treatments the heavy microsome fraction was the only significantly different cell component in which the heavy microsomes from resistant fish retained more 14C-DDT than those from susceptible fish. For the in vitro treatments all liver fractions from susceptible fish showed a significantly greater retention than did those from resistant fish.