Environmental salinity regulates receptor expression, cellular effects, and circulating levels of two antagonizing hormones, 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3, in rainbow trout.
In freshwater-adapted rainbow trout, intestinal cells (enterocytes) possess receptors for 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] in the basolateral membrane, and respond to treatment with 1,25(OH)(2)D(3) with increased intracellular calcium concentrations. No receptors are found for the antagonizing hormone 24,25-dihydroxyvitamin D(3) [24,25(OH)(2)D(3)] at the enterocyte basolateral membrane, and it has no effect on enterocyte calcium homeostasis. After acclimation to seawater, however, the enterocyte membrane receptors for 1,25(OH)(2)D(3) are down-regulated and specific binding for 24,25(OH)(2)D(3) appears, which is further up-regulated with time spent in seawater. This shift in receptor expression is concurrent with an increased sensitivity of the enterocytes to 24,25(OH)(2)D(3) and a decreased sensitivity to 1,25(OH)(2)D(3). This results in a partial inhibition of intracellular calcium uptake, which would be beneficial when inhabiting a calcium-rich environment like seawater.
Larsson
Dennis
D
Fish Endocrinology Laboratory, Department of Zoology/Zoophysiology, Göteborg University, SE-405 30 Göteborg, Sweden. dennis.larsson@zool.gu.se
Nemere
Ilka
I
Aksnes
Lage
L
Sundell
Kristina
K
D015650:24,25-Dihydroxyvitamin D 3 / Q000097:blood*; D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D020895:Enterocytes / Q000378:metabolism*; D004777:Environment; D005260:Female; D005618:Fresh Water; D006706:Homeostasis / Q000502:physiology; D008297:Male; D017686:Oncorhynchus mykiss / Q000502:physiology*; D018167:Receptors, Calcitriol / Q000378:metabolism; D012623:Seawater
C031424:24,25-dihydroxycholecalciferol receptor; D018167:Receptors, Calcitriol; D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol; D002118:Calcium