In vivo and in vitro cadmium accumulation during the moult cycle of the male shore crab Carcinus maenas—interaction with calcium metabolism

Abstract

The effect of moult stage on cadmium accumulation and distribution was investigated in vivo in male shore crabs Carcinus maenas exposed to 1 mg Cd l −1 for 7 days. The accumulation of cadmium in all tissues examined was markedly higher in postmoult (A 1–2 and B 1–2) compared to intermoult (C 1, C 3 and C 4) and premoult (D 0–3). In addition, elevated levels of cadmium were found in gills of late premoult (D 2–3) animals. The total amount of cadmium accumulated in the tissues (haemolymph, gills, midgut gland and muscle) increased from 43 μg Cd in early premoult (D 0–1) to 391 μg Cd in late postmoult (B 1–2). Gills and midgut gland were the primary cadmium accumulating tissues in C 4-intermoult and premoult (D 0–3); in early postmoult (A 1–2) haemolymph and midgut gland were the main cadmium containing tissues, while midgut gland dominated in late postmoult (B 1–2) and early intermoult (C 1 and C 3). A detailed account of calcium distribution in haemolymph, gills, midgut gland, muscle and exoskeleton during the moult cycle is presented. Mechanistic links between cadmium and calcium uptake in posterior gills of C 4-intermoult and early postmoult (A 1–2) crabs were explored using an in vitro gill perfusion technique. Calcium and cadmium influxes were markedly higher in postmoult compared to intermoult. No differences between intermoult and postmoult effluxes were found for either calcium or cadmium. From intermoult to postmoult net influx increased from 2.4 to 29 μmol Ca 2+ g −1 ww gill h −1 and from 0.24 to 25 nmol Cd 2+ g −1 ww gill h −1. The results indicate that the postmoult increase in cadmium influx is due to increased active transport of cadmium, at least partly, by accidental uptake via calcium transporting proteins. The in vitro net influx rates corresponded accurately to the observed in vivo accumulation of both cadmium and calcium. Although cadmium accumulation and distribution are clearly linked to changes in calcium requirements, cadmium did not interfere with calcium accumulation or distribution at any stage during the moult cycle.