Neuronal cholinergic control is involved in the modification of cardiac activity and circulation induced by waterborne copper in the chiton Acanthopleura japonica

Abstract

Cardiac activity and arterial throughput were studied in the chiton Acanthopleura japonica following exposure to waterborne copper. In order to understand the mechanism of copper action, exposure to the metal was combined with injection of the sodium channel blocker tetrodotoxin, and two cholinergic antagonists, atropine and benzoquinonium. Copper (0.25, 0.33, 0.5, 1 mg l − 1 ; 3 h) induced a concentration dependent reduction in heart rate and, at the highest concentration, a reversible arrest of heartbeat. Tetrodotoxin (1 μM), atropine (20 μM) and benzoquinonium (5 μM) significantly antagonized the reduction in heart rate elicited by copper (0.33 mg l − 1 , 3 h). As copper also induced a reduction of heartbeat amplitude and consequent arterial throughput, these results support the hypothesis that the metal activates an extrinsic cholinergic control of heart activity in chitons, resulting in a decrease in haemolymph circulation and, consequently, of metal uptake through the gills.