Ocean acidification: effects of pH on 45 Ca uptake by lobster branchiostegites

• Published in: Journal of Comparative Physiology B
• Main Authors: Nagle, Lilian, Brown, Skye, Krinos, Arianna, Ahearn, Gregory A.
• Format: Text
• Language: unknown
• Published: UNF Digital Commons 2018
• Subjects: Amiloride; Antiport; Branchiostegites; Calcium transport; Climate change; Competitive inhibition; Homarus americanus; Lobster; Membrane potential; Ocean acidification; Proton inhibition; Verapamil
• Online Access: https://digitalcommons.unf.edu/unf_faculty_publications/1492; https://doi.org/10.1007/s00360-018-1173-2

Gill chambers of the Atlantic lobster, Homarus americanus, possess three structures that are involved with respiration and ion regulation: gill filaments, epipodites, and branchiostegites. This paper describes ion transport mechanisms present in the plasma membranes of branchiostegite epithelial cells and the effects of pH on the uptake of 45Ca by these processes. Partially purified membrane vesicles (PPMV) of branchiostegite cells were produced by a homogenization/centrifugation method that has previously been used to define ion transport processes in both crab and lobster gill tissues. In the present study, lobster branchiostegite PPMV 45Ca uptake was highest at pH 8.5 and lowest at pH values between 6.0 and 7.0 (p < 0.02). At pH 8.0, 45Ca uptake was a biphasic process consisting of a saturable process at low [Ca] and a linear process at higher [Ca]. At pH 6.0, 45Ca uptake was only a linear process and paralleled linear uptake at pH 8.0. A valinomycin/K+-induced membrane potential (PD, inside negative) doubled 45Ca uptake at pH 7.0 above that in the absence of a PD (p < 0.05). An induced PD at pH 8.0 did not significantly (p > 0.05) affect 45Ca uptake observed in the absence of a PD, but was threefold greater than uptake at pH 7.0 in the absence of a PD (p < 0.05). Amiloride (2 mM) did not affect 45Ca uptake at pH 8.0, but 2 mM amiloride + 100 µM verapamil reduced uptake by approximately 50%. In the presence of both 2 mM amiloride + 100 µM verapamil, 15 s 45Ca influx at pH 8.5 was a hyperbolic function of [Ca] (0.1–5 mM) (Km = 4.2 ± 0.3 mM; Jmax = 9792 ± 439 pmol/mg protein × 15 s). 45Ca influxes at pH 7.5 under the same conditions were also hyperbolic with Km = 8.3 ± 1.4 mM; Jmax = 10732 ± 1250 pmol/mg protein × 15 s. Km values were significantly different (p < 0.05), but Jmax values were not (p > 0.05). These results suggest that 45Ca uptake by lobster branchiostegites may have occurred by the combination of diffusion through a verapamil-inhibited calcium channel and carrier-mediated ...