Post-Moult Calcification in the Blue Crab (Callinectes Sapidus): Relationships between Apparent Net H+ Excretion, Calcium and Bicarbonate

Abstract

In the days immediately after moulting, manipulations of external pH, [HCO3−], and [Ca2+] were used to determine the nature of the rapid net Ca2+ influx and attendant apparent net H+ efflux in the blue crab (Callinectes sapidus Rathbun). Both fluxes were strongly inhibited by reductions in external [Ca2+], [HCO3−], or pH. The net Ca2+ influx was reversed at an external concentration of 2.5 mmol l−1, and both fluxes were reversed by reducing the external [HCO3−] to 0.2 mmol l−1. The correlation between net Ca2+ flux and apparent net H+ flux was 0.61 (P<0.01), but the variability and the time course of most experiments indicated that the link was indirect, rather than a direct coupling or cotransport. This conclusion was also borne out by acid-base disturbances that occurred in the low-[Ca2+] treatment. The results are consistent with the hypothesis that inward calcium transport is accompanied by both inward HCO3− transport and outward H+ transport, probably by separate exchanges with ions of like charge such as Na+ and Cl−. Crustecdysone (β-ecdysone) does not appear to be involved in control of these post-moult fluxes and calcification.