The influence of external calcium in facilitating copper-induced contraction in the isolated siphon of Scrobicularia plana (Bivalvia)

The estuarine bivalve S. Plana responds to the application of copper or zinc and the action of these ions has been further investigated by use of an isolated inhalant siphonal preparation. The experiments described in this paper were, designed to test whether the presence of external calcium in necessary for copper to elicit siphonal contractions. The effects of various copper concentrations. on the siphonal preparation of S. plana were studied by addition of copper to artificial sea water (ASW) as described by Kobayashi. ASW was also made up with the omission of CaC1 sub(2) (Ca-free ASW) and accompanied by adjustments in the amount of NaC1 to make all solutions isotomic. The time required for the absence of calcium to have an effect was further determined by placing siphonal preparations in Ca-free ASW and applying electrical stimuli (Square pulses-each of 5V and 5mS duration.