EFFECTS OF ABAMECTIN ON INTRACELLULAR POTASSIUM-ION ACTIVITY AND MEMBRANE-POTENTIAL IN DIPTERAN SKELETAL-MUSCLE

The effects of abamectin (AVMB1) on intracellular potassium ion activi ty (aK1) and resting membrane potential (E(m)) of the skeletal muscle cells of final instar larvae of Phormia terraenovae (Diptera) were inv estigated using K+-selective micro-electrodes. Bathing the preparation in 10(-6) mAVMB1 (+1 ml litre-1 dimethylsulfoxide) for 60 min caused a significant (31 %) decrease in aK1, whilst E(m) depolarized on avera ge by 19 mV (nearly 50 % of the original control value). The differenc e E(K) - E(m) increased by 9 mV, although E(K) (potassium equilibrium potential) remained more negative than E(m). These results could be du e to a cationic effect of AVMB, possibly involving an increase in K+ a nd Na+ conductances of the muscle plasma membrane.