Effect of avermectins on Ca2+-dependent Cl- currents in plasmalemma of Chara corallina cells

A natural complex of avermectins, aversectin C, and a component of this complex, avermectin A(1), were shown to change the conductivity of Ca2+- dependent Cl- channels of plasmalemma of Chara corallina cells by acting from the outer side of the cellular membrane. Low concentrations of aversectin C and avermectin A, increased the Cl- current: K-1/2 = 35 ng/ mi for the whole complex and K-1/2 = 21 pglml for A(1). Relatively high concentrations of the compounds suppressed the Cl- current. K-1/2 = 2.2 mug/ml for aversectin C and K-1/2 = 4.2 ng/ml for A(1). The Hill coefficient for the interaction of avermectin A, with the corresponding targets was identical for stimulation and suppression of the Cl- current: 2.8 and 2.5, respectively. Bicuculline, a nonspecific inhibitor of the GABA, receptors, did not influence stimulation of Cl- currents caused by low concentrations of avermectins, but at the same time blocked suppression of the Cl- currents by high concentrations of avermectins. Avermectins A(2), B-1. B-2 abamectin and 22,23-dihydroavermectin B-1 (ivermectin) did not affect the Cl- currents of Chara corallina cells.