[Effect of avermectns on Ca(2+)-dependent chloride currents in plasmalemma of Chara corallina cells]

A natural complex of avermectins, aversectin C, and a component of this complex, avermectin A1, were shown to change the conductivity of Ca(2+)-dependent chloride channels of plasmalemma of Chara corallina cells by acting only from the outer side of the cellular membrane. Low concentrations of aversectin C and avermectin A1 increased the chloride current: K1/2 = 3.5 x 10(-5) mg/ml for the whole complex and K1/2 = 2.1 x 10(-3) mg/ml for A1. Relatively high concentrations of the compounds suppressed the chloride current: K1/2 = 2.2 x 10(-3) mg/ml for aversectin C and K1/2 = 4.2 x 10(-6) mg/ml for A1. The Hill coefficients for the interaction of avermectin A1 with the corresponding targets for stimulation and suppression of the chloride current were 2.8 and 2.5 respectively. Bicuculine, a non-specific inhibitor of the GABA alpha-receptors, did not influence stimulation of chloride currents caused by action of low concentrations of avermectins, but at the same time blocked suppression of the chloride currents associated with the action of high doses of avermectins. Avermectins A2, B1 (abamectin), B2 and 22,23-dihydroavermectin B1 (vermectin) in the concentration range studied, did not affect the chloride currents of Chara corallina cells.