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.

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Hogstrand, Christer, P ieter M. Verbost, Sjoerd E. Wendelaar B onga, and Chris M. Wood. Mechanisms of zinc uptake in gills of freshwater rainbow trout: interplay with calcium transport. Am. J. Physiol. 270 (.Regulatory Integrative Comp. Physiol. 39): R1141-R1147, 1996.-The uptake mechanism of Zn2+ through the gill epithelium of freshwater rainbow trout was investigated both in intact animals and in isolated basolateral membranes. Involvement of the apical Ca2+ uptake sites in Zn2+ uptake was examined in vivo by pharmacological manipulation of the apical Ca2+ permeability. The apical entries of Ca2+ and Zn2+, but not Na+ and Cl-, were inhibited by addition of La to the water. Addition of 1.0 pM La reduced the influxes ofCa2+ and Zn2+ to 22 ± 3 and 53 ± 7% (means ± SE) of the control value, respectively. Injection of CaCl2 also reduced the branchial influxes of Ca2+ and Zn2+. This treatm ent decreased the influx of Ca2+ to 45 ± 4% of the control level and the Zn2+ influx to 6 8 ± 5%. These results strongly imply th a t Zn2+ passes across the apical membrane of the chloride cells of the gills via the same pathway as Ca2+. The presence of an active basolateral transporter for Zn2+ was investigated in vitro on isolated basolateral membranes. There was no ATP-dependent or N a+-gradient driven transport of Zn2+ at physiologi cal Zn2+ activities. The same system was used to study potential effects ofZn2+ on the basolateral Ca2 +-adenosinetriphosphatase. Zn2+ was found to be a potent blocker of this transporter, causing a mixed inhibitory effect on the ATPdriven Ca2+ transport at a free Zn2+ activity of 100 pM.

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SummaryA thienopyr(im)idine (Org41841) activates the LH receptor but does not compete with the natural ligand binding site and does not show agonistic action on the follicle-stimulating hormone receptor (hFSHR) at sub-millimolar concentrations. When this drug is preincubated at sub-micromolar concentrations with host cells expressing the hFSHR, and then washed out, binding analysis and assessment of receptor-effector coupling show that it increases plasma membrane expression of the hFSHR. Real time PCR shows that this effect did not result from increased hFSHR mRNA accumulation. It is possible that Org41841 behaves as a pharmacoperone, a drug which increases the percentage of newly synthesized receptor routing to the membrane. Like pharmacoperones for other receptors, this drug was able to rescue a particular mutant hFSHR (A 189 V) associated with misrouting and endoplasmic reticulum retention, although other mutants could not be rescued. This is potentially the first member of the pharmacoperone drug class which binds at a site that is distinctive from the ligand binding site.