Ocean acidification: synergistic inhibitory effects of protons and heavy metals on 45 Ca uptake by lobster branchiostegite membrane vesicles

• Published in: Journal of Comparative Physiology B
• Main Authors: An, Dalen, Husovic, Aida, Ali, Laeequa, Weddle, Elizabeth, Nagle, Lilian, Ahearn, Gregory A.
• Format: Text
• Language: unknown
• Published: UNF Digital Commons 2019
• Subjects: Antiport; Branchiostegites; Calcium transport; Climate change; Competitive inhibition; Divalent cations; zinc; copper; cadmium; Electroneutral Ca /2H exchange 2+ +; Gills; Homarus americanus; Ion channel; Lobster; Membrane vesicles; Ocean acidification; Pollution; Verapamil
• Online Access: https://digitalcommons.unf.edu/unf_faculty_publications/820; https://doi.org/10.1007/s00360-019-01227-7

Previous work with isolated outer membrane vesicles of lobster branchiostegite epithelial cells has shown that 45Ca2+ uptake by these structures is significantly (p < 0.02) reduced by an incremental decrease in saline pH (increased proton concentration) and that this decrease is due to competitive inhibition between carrier-mediated transport of 45Ca2+ and hydrogen ions. The present paper extends these previous findings and describes the combined effects of pH and cationic heavy metals on branchiostegite uptake of 45Ca2+. Partially purified membrane vesicles of branchiostegite cells were produced by a homogenization/centrifugation method and were loaded with mannitol at pH 7.0. The time course of 1 mM 45Ca2+ uptake in a mannitol medium at pH 8.5 containing 100 µM verapamil (Ca2+ channel blocker) was hyperbolic and approached equilibrium at 30 min. This uptake was either significantly reduced (p < 0.05) by the addition of 5 µM Zn2+ or essentially abolished with the addition of 5 µM Cu2+. Increasing zinc concentrations (5–500 µM) reduced 1 mM 45Ca2+ uptake at pH 8.5 or 7.5 in a hyperbolic fashion with the remaining non-inhibited uptake due to apparent non-specific binding. Uptake of 1 mM 45Ca2+ at pH 8.5, 7.5, 7.5 + Zn2+, and 7.5 + Zn2+ + Cu2+ + Cd2+ in the presence of 100 µM verapamil displayed a stepwise reduction of 45Ca2+ uptake with the addition of each treatment until only non-specific isotope binding occurred with all cation inhibitors. 45Ca2+ influxes (15 s uptakes; 0.25–5.0 mM calcium + 100 µM verapamil) in the presence and absence of 10 µM Zn2+ were both hyperbolic functions of calcium concentration. The curve with Zn2+ displayed a transport Km twice that of the control (p < 0.05), while inhibitor and control curve Jmax values were not significantly different (p > 0.05), suggesting competitive inhibition between 45Ca2+ and Zn2+ influxes. Analysis of the relative inhibitory effects of increased proton or heavy metal interaction with 45Ca2+ uptake suggests that divalent metals may reduce the ...