Calcium transport in gill cells of Ucides cordatus, a mangrove crab living in variable salinity environments

Crustaceans show discontinuous growth and have been used as a model system for studying cellular mechanisms of calcium transport, which is the main mineral found in their exoskeleton. Ucides cordatus, a mangrove crab, is naturally exposed to fluctuations in calcium and salinity. To study calcium transport in this species during isosmotic conditions, dissociated gill cells were marked with fluo-3 and intracellular Ca2 + change was followed by adding extracellular Ca2 + as CaCl2 (0, 0.1, 0.25, 0.50, 1.0 and 5 mM), together with different inhibitors. For control gill cells, Ca2 + transport followed Michaelis-Menten kinetics with Vmax = 0.137 ± 0.001 ∆Ca2 +i (μM × 22.104 cells− 1 × 180 s− 1; N = 4; r2 = 0.99); Km = 0.989 ± 0.027 mM. The use of different inhibitors for gill cells showed that amiloride (Na+/Ca2 + exchange inhibitor) inhibited 80% of Ca2 + transport in gill cells (Vmax). KB-R, an inhibitor of Ca influx in vertebrates, similarly caused a decrease in Ca2 + transport and verapamil (Ca2 + channel inhibitor) had no effect on Ca2 + transport, while nifedipine (another Ca2 + channel inhibitor) caused a 20% decrease in Ca2 + affinity compared to control values. Ouabain, on the other hand, caused no change in Ca2 + transport, while vanadate increased the concentration of intracellular calcium through inhibition of Ca2 + efflux probably through the plasma membrane Ca2 +-ATPase. Results show that transport kinetics for Ca2 + in these crabs under isosmotic conditions is lower compared to a hyper-regulator freshwater crab Dilocarcinus pagei studied earlier using fluorescent Ca2 + probes. These kinds of studies will help understanding the comparative mechanisms underlying the evolution of Ca transport in crabs living in different environments.