Regulation of calcium balance in the sturgeonAcipenser naccarii: a role for PTHrP

Abstract

Calcium regulation in sturgeon is of special interest because they are a representative of the ancient fishes possessing mainly cartilaginous skeletons and a supposedly low calcium demand. The present study aimed to characterize the effect of a chronic absence of dietary calcium and the effect of parathyroid hormone-related protein (PTHrPA) (1-34) (7) on calcium balance in juvenile sturgeon (Acipenser naccarii). At rest, sturgeon juveniles are in net positive calcium balance, since whole body calcium uptake is significantly higher than efflux and calcium accumulates in the body. To study the importance of dietary calcium, the sturgeon were kept on a calcium-free diet for 8 wk. This manipulation impaired growth as measured by failure to gain weight or increase in length and indicates that dietary calcium is important for growth in sturgeon. An increased whole body calcium uptake partially compensated dietary calcium deficiency and was associated with increased gill chloride cell number in lamellae and filaments in parallel with increased gill Na(+)K(+)-ATPase activity. In addition, a single injection of piscine PTHrP(1-34) significantly increased whole body calcium uptake and decreased whole body calcium efflux. Administration of PTHrP significantly increased circulating plasma calcium 4-24 h postinjection. The increase in net calcium transport and increased plasma levels of calcium is consistent with the actions of a hypercalcemic factor. It would appear that the sturgeon rely on calcium for growth and tightly regulate calcium transport. The action in calcium balance is consistent with PTHrP acting as a hypercalcemic factor in sturgeon.

Parathyroid hormone-related protein-stanniocalcin antagonism in regulation of bicarbonate secretion and calcium precipitation in a marine fish intestine

“…5). The results obtained are in agreement with previous in vivo (2,10,11,19) and in vitro (9) results and indicate a mechanism consistent with hypercalcemic actions of PTHrP in fish.…”

The influence of environmental calcium concentrations on calcium flux, compensatory drinking and epithelial calcium channel expression in a freshwater cartilaginous fish

“…This relationship has also been found in the developing stages of other fishes (Chou et al, 2002;Flik et al, 1986;Flik et al, 1985;Fuentes et al, 2007). Thus, lake sturgeon seem very capable of handling low calcium environments, at least at the concentrations tested, although there may be a lower limit of tolerable Ca 2+ concentrations.…”

“…In this study, lake sturgeon responded to low environmental calcium concentrations by increasing Ca 2+ uptake and decreasing efflux, whereas in high environmental calcium concentrations the opposite was true. Ca 2+ influx rates in lake sturgeon were lower than those reported in freshwater-acclimated larval tilapia [200-250nmolg -1 h -1 (Chou et al, 2002;Hwang et al, 1996)], comparable to those reported in juvenile tilapia [~110nmol h -1 g -1 ; Flik et al (Flik et al, 1986);Flik et al (Flik et al, 1985)], and higher than those reported from juvenile rainbow trout [30-60nmolh -1 g -1 (Hogstrand et al, 1994;Niyogi and Wood, 2006) (Flik et al, 1986;Flik et al, 1985)], and higher than those in Adriatic sturgeon [~1nmolh -1 g -1 (Fuentes et al, 2007)]. In this study, it is likely that acclimation time also influenced the magnitude of Ca 2+ -influx, as influx rates in rainbow trout (Oncorhynchus mykiss) subjected to low calcium environments have been demonstrated to be initially high, and to gradually decrease with the duration of acclimation (Perry and Wood, 1985).…”

Zebrafish Bone and General Physiology Are Differently Affected by Hormones or Changes in Gravity

“…PTH administration induced hypercalcemia in fugu ( Tetraodon nigrividans ) by inducing both osteoblast and osteoclast function and by decreasing scale calcium content [94]. Genes homologous to the mammalian PTH-related peptides (PTHrP) were found in teleosts, they are more widely expressed [95], they increase calcium uptake in sturgeon ( Acipenser nacarii ) [96]and were shown to play different roles in craniofacial development in zebrafish [97]. Blocking PTH signaling through the use of a PTH/PTHrP antagonist resulted in a decreased hypercalcemic response to estradiol in sea bream ( Sparus aurata ) [98].…”