Mechanisms of Ca Uptake in Freshwater and Seawater-acclimated Killifish, Fundulus Heteroclitus, and Their Response to Acute Salinity Transfer

Overview

Journal J Comp Physiol B

Specialties Biochemistry
Endocrinology
Physiology

Date 2018 Dec 6

PMID 30515571

Citations 4

Authors

Alex M Zimmer

Kevin V Brix

Chris M Wood

Affiliations

Soon will be listed here.

Abstract

Killifish (Fundulus heteroclitus) has been extensively used as a model for ion regulation by euryhaline fishes. Na and Cl dynamics have been well studied in killifish, but few studies have addressed that of Ca. Therefore, this study aimed to characterize Ca fluxes in freshwater (FW) and seawater (SW)-acclimated killifish, their response to salinity transfer, and to elucidate the mechanisms of Ca influx in FW and SW. SW killifish displayed a significantly higher Ca influx rate than that of FW fish, while Ca efflux rates were comparable in both salinities. Ca influx was saturable in FW (K = 78 ± 19 µmol/L; J = 53 ± 3 nmol/g/h) and influx by SW killifish was linear up to 7 mmol/L Ca. In SW-acclimated fish, 36% of Ca influx was attributed to "intestinal Ca intake", likely caused by drinking, whereas intestinal Ca intake in FW contributed to < 2% of total. Throughout the study, results suggested that "cation competition" in SW modulates Ca influx. Therefore, we hypothesized that SW-acclimated fish actually have a higher affinity Ca influx system than FW-acclimated fish but that it is competitively inhibited by competing SW cations. In agreement with this cation competition hypothesis, we demonstrated for the first time that "extra-intestinal" Ca influx was inhibited by Mg in both FW and SW-acclimated killifish. Following acute salinity transfer, extra-intestinal Ca influx was rapidly regulated within 12-24 h, similar to Na and Cl. Ca influx in FW was inhibited by La, an epithelial Ca channel blocker, whereas La had no significant effect in SW.

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