Ultrastructural evidence of calcium uptake by chloride cells in the gills of goldfish, Carassius auratus

Abstract

Calcium uptake by the gills in goldfish (Curussius uurutus) was observed by electron microscopy using an oxalate-based method which specifically induced electron-opaque precipitates in association with chloride cells in the primary epithelium. EDTA treatment and x-ray microanalysis substantiated that these precipitates are a calcium salt. They were never found in deionized-water-adapted fish. Oxalate-induced calcium precipitates, varying from 0.04 to 0.2 pm in diameter, occurred in the apical crypts of chloride cells and in large vacuole-like structures in the lateral and basolateral regions of the cells. The crypts where the precipitates arose scatteringly had the morphological characteristics similar to the normal morphology of apical crypts: they were 2 to 4 pm in diameter and lined with darker and homogeneous cytoplasm with microridges. The vacuole-like structures containing numerous calcium precipitates were somewhat irregular in contour and had a diameter of about 3 pm. They appeared to contact a densely distributed tubular system, but their limiting membrane was uncertain in the present resolution. The precipitates were concentrated in the central region of the structures. These results suggest that branchial calcium uptake is closely associated with chloride cells in goldfish.

Characterization of a branchial epithelial calcium channel (ECaC) in freshwater rainbow trout (Oncorhynchus mykiss)

“…According to current models, the MRC of the gill is the principal cell type involved in Ca 2+ uptake (Ishihara and Mugiya, 1987;Perry and Flik, 1988;Fenwick, 1989;McCormick et al, 1992;Marshall et al, 1992;Flik et al, 1995;Flik et al, 1996;Li et al, 1997;Moron et al, 2003). In apparent disagreement with the putative model, the results presented in this study suggest that MRCs are neither the sole, nor the primary cell types expressing ECaC, which is thought to represent the initial step in Ca 2+ absorption across the gill.…”

“…AY256348). On the basis of extensive but largely correlative data (Perry and Wood, 1985;Ishihara and Mugiya, 1987;Perry and Flik, 1988;Perry et al, 1992;Marshall et al, 1992;McCormick et al, 1992;MacKenzie and Perry, 1997), a model has been developed in which the branchial mitochondriarich cell (MRC; also termed ionocyte or chloride cell) is the principal site of transepithelial Ca 2+ uptake in freshwater fish (Perry, 1997;Marshall, 2002;Evans et al, 2005).…”

Calcium uptake in the skin of a freshwater teleost.

“…However, MR cells are often termed "chloride cells", even when found in freshwater-adapted teleost, where a Cl-secretory function is unlikely and a Cl-uptake function is uncertain (for reviews of MR cell structure and function, see refs. [35][36][37] (6,38), although conflicting evidence exists (14). Perry (6)(7)(8)(9)(10)(11)(12), although the possibility of other active transport pathways has not been ruled out.…”

Hormonal and environmental regulation of epithelial calcium channel in gill of rainbow trout (Oncorhynchus mykiss)

“…On the basis of these and other indirect or correlative studies (18,26,28,32), a model was constructed (27) in which the MRC was implicated as the principal (potentially exclusive) cell type responsible for Ca 2ϩ uptake. In the present study, however, immunocytochemical analysis of gill cross sections in fish exposed to soft water failed to demonstrate strong colocalization of Na ϩ /K ϩ -ATPase (representative of MRCs) and ECaC-positive cells (Fig.…”

“…It has been suggested that fish ECaC and TRPV subfamilies diverged prior to a possible gene duplication giving rise to TRPV5 and TRPV6 (35). Although the site of Ca 2ϩ uptake in freshwater fish is believed to be the chloride cell (also termed mitochondria-rich cell, MRC) (18,23,24,27,28,32), ECaC appears to be ubiquitously expressed in all of the gill epithelial cell types, including pavement cells (PVCs) and chloride cells (35).…”