CATION BALANCE IN CRUSTACEAN HEMOLYMPH - RELATIONSHIP TO CELL-MEMBRANE POTENTIALS AND MEMBRANE-SURFACE CHARGE

Data were compiled on K+, Na+, Mg2+ and Ca2+ in haemolymph of 74 speci es of Malacostraca and three freshwater species of Anostraca. Mean [K] is positively correlated with both mean [Na+] and mean [Mg2+]. Mean [Mg2+] and [Na+] are themselves positively correlated. Mean [Ca2+] sho ws little correlation with the others, except that concentrations of a ll four cations are low in the Anostraca. The data suggest that haemol ymph composition has evolved in such a way as to preserve the transmem brane potential across particular areas of cell membrane, this being d etermined by constant transport and permeability properties for K+, Na + and Ca2+, and by superficial fixed negative charges of constant dens ity (about 1 e/nm(2) on the outer surface).