The effects of cadmium (Cd2+) on calcium (Ca2+) transport in the gills of rainbow trout (Salmo gairdneri) were studied. The gill epithelium of freshwater fish represents a model for a Ca2+-transporting tight epithelium. Unidirectional Ca2+ fluxes in the gills were estimated in an isolated saline-perfused head preparation. Ca2+ influx was not affected when up to 10 microM Cd were added to the ventilatory water at the start of flux determinations (in vitro exposure). However, after 16 h in vivo preexposure of the fish to 0.1 microM Cd in the water, a 79% inhibition of Ca2+ influx was observed. Ca2+ efflux was not affected when up to 10 microM Cd were added to the ventilatory water during the flux determination. Ca2+ efflux in fish preexposed to 0.1 microM Cd for 16 h was also not affected; a preexposure to 1 microM Cd, however, resulted in a 173% increase in Ca2+ efflux rates. Tracer retention in the gill tissue indicated that both Ca2+ and Cd2+ enter the gill epithelium via a lanthanum (La3+)-inhibitable pathway. It is concluded that Cd2+ readily enters the branchial epithelial cells, similarly as Ca2+ does via La3+-sensitive apical Ca2+ channels. The inhibitory action of Cd2+ on transepithelial Ca2+ influx seems to result from an inhibition of the basolateral Ca2+ transport, occurring after a critical intracellular Cd2+ concentration has been reached.

No abstract

A ïstract. The skin structure and the plasma cortisol leve of trout, Oncorhynchus m ykiss, were examined durii : 7 days of exposure to water of pH 5. By day-4 and -7 the thickness of the epidermis was significantly (/ <0.05) less in acid exposed fish than in controls, and cl generative cells were common in the upper epidermal I; ers. Many epidermal cells exhibited signs of necrosis, a 1 by day-7 many apoptotic cells were also present. Seci tory vesicles of high electron density were abundant h the filament cells of the 3-4 outermost layers of epid mis, and intercellular spaces had increased. Mitotic Il Lires occurred throughout the epidermis, with the exc uion of the outermost cell layer. Mucous cells became e »ngated after day-1, and later, newly differentiating n icous cells could be seen close to the skin surface, and n my mucocytes contained mucosomes of high electron d isity. Rodlet cells were occasionally seen. Chloride c Is appeared similar to those of control fish. Many leuc cytes, mainly macrophages and lymphocytes, had pene ated the epidermis via the highly undulating basal k nina, and at day-7, numerous apoptotic lymphocytes w re found. In the dermis, melanosomes became disp rsed in the cytoplasmic extensions of melanocytes w lich were present in the epidermis of all acid-exposed fi h. Iridocytes were rare after day-4, while fibroblasts w re abundant and secreted larçe amounts of collagen. A ter 1 day of exposure to acidified water, a significant (/ <0.05) elevation of the plasma cortisol level had occ rred, but this subsequently declined, and had returned u control values by day-7. The changes in skin struce, however, remained throughout the whole exposure period.

Enterobacter cloacae (strain DF1 3) was found to produce a bacteriocin which could be induced by mitomycin C. In the supernatant fluid of the induced culture phagelike particles were found. The bacteriocin was partially purified from induced cultures by ammonium sulfate precipitation and gel-filtration on Sephadex G-150. Ultraviolet-absorbing material was eluted from the Sephadex column in three fractions. The biological activity was mainly present in the second fraction and is associated with a protein with a molecular weight of about 61,000. The phagelike particles were found in the first fraction and show no biological activity. Upon conjugation of E. cloacae strain DFI 3 with another strain of the same species and with Escherichia coli K-12S, the ability to produce bacteriocin was transferred. The new bacteriocinogenic strain produced bacteriocin, which could not be distinguished from that produced by E. cloacae strain DF13. Although transfer of the bacteriocinogenic factor often occurred together with transfer of the ability to produce phagelike particles, it was shown that these two factors are two separate genetic entities. In addition to a bacteriocinogenic factor, E. cloacae strain DF13 was found to carry two other transferable plasmids: one determining resistance against streptomycin and sulfanilamide and another determining resistance against penicillin.

In vivo treatment with external bafilomycin A(1), a selective inhibitor of V-ATPase H(+) pumps, reduced whole-body Na(+) influx by up to 90 % in young tilapia and 70 % in young carp. The inhibition was rapidly reversible, with whole-body Na(+) influx rebounding to 280 % of pre-treatment values within 20 min of removal from the bafilomycin. This rebound effect is consistent with the prior accumulation of protons during the period when the cells were exposed to bafilomycin. Bafilomycin also inhibited Cl(−) uptake, an effect that was still apparent 30 min after the removal of bafilomycin. These data provide circumstantial evidence for previous suggestions that Na(+) uptake in freshwater fish is associated with a proton-motive force created by a proton pump and indirect evidence for the major significance of this mechanism in the branchial uptake of Na(+) by freshwater fish.