Detection of a P-glycoprotein related pump in Chironomus larvae and its inhibition by verapamil and cyclosporin A

A membrane associated ATP-dependent efflux pump, similar in function to mam malian P-glycoprotein, was detected in anal papillae of Chironomus riparius larvae. Immunohistochemical analysis of larval tissues, using monoclonal a ntibodies against P-glycoprotein, was supplemented by functional in vivo an d in vitro assays which confirmed the existence of a mechanism for transpor ting xenobiotic substances. The in vitro ATPase activity of homogenate frac tions increased in the presence of typical P-glycoprotein substrates (vinbl astine, actinomycin D or ivermectin). This increase was unaffected by inhib itors of other membrane ATPases (sodium azide, EGTA, ouabain). but sensitiv e to vanadate, cyclosporin A and verapamil which inhibit mammalian P-glycop rotein mediated ATP-consumption. Sublethal concentrations of specific P-gly coprotein-inhibitors such as verapamil or cyclosporin A synergistically enh anced the mortality of C. riparius towards ivermectin. Although cyclosporin A originates from entomopathogenic fungi, its mode of action in insects an d its function during infection are not understood. Our results lend some c redit to the hypothesis that this compound is possibly released to promote poisoning of the infected host by xenobiotics which are normally removed by a P-glycoprotein related pump. The putative role of insect P-glycoprotein homologues in the contest of multiple resistance towards insecticides is di scussed. (C) 1998 Elsevier Science inc. All rights reserved.