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Endocrinology of calcium homeostasis
General and Comparative Endocrinology 152 (2007) 242 www.elsevier.com/locate/ygcen
Discussion
Endocrinology of calcium homeostasis Adelino Canario a, Gert Flik a b
b
Centre of Marine Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal Faculty of Science, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
Michelle Wheatly reviewed the role of binding proteins in the regulation of calcium homeostasis during periods of net vectorial influx using the crayfish, Procambarus clarkii, as a model. The proteins studied were the import and export proteins, epithelial Ca2+ channel (ECaC), sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), plasma membrane Ca2+ ATPase (PMCA) and Na+/Ca2+ exchanger (NCX). The expression of these proteins is a coordinated process at multiple levels including the apical vs. basolateral domains, plasma membranes vs. organelle membranes and transmembrane Ca2+ transporters and binding proteins. An integrative model of cellular Ca2+ homeostasis was presented which took into account the spatial and temporal protein expression during crayfish molting. Kristina Sundell presented a comparative account of Ca2+ regulation by vitamin D3 starting from the classical view that the vitamin D3 system evolved during the water to land transition in response to a scarcity of Ca2+ in the terrestrial environment. By comparing Ca2+ metabolism in freshwater (FW) and seawater (SW) fishes, it has been possible to establish conserved features, such as vitamin D3 metabolism and nuclear receptors, as well as rapid non-genomic divergent responses to 1,25(OH)2-vitamin D3 (calcitriol) and 24,25(OH)2-vitamin D3 mediated by membrane receptors, which appear to be dependent on Ca2+ availability. In the Free Communications Gert Flik showed that in the marine fish gilthead sea bream (Sparus aurata) only in conditions of Ca2+ deficiency in the water and in the diet, were plasma Ca2+ and parathyroid hormone-related protein (PTHrP) decreased. It was hypothesized that PTHrP may have a paracrine action to regulate branchial Ca2+ handling. Positive correlations between plasma PTHrP, calcium, phosphorus and magnesium may indicate a role
0016-6480/$ - see front matter Ó 2007 Published by Elsevier Inc. doi:10.1016/j.ygcen.2007.05.023
for the hormone in bone development. Finally, PTHrP potentiates estradiol-induced vitellogenesis in cultured hepatocytes hinting at a multiple role for the protein in fishes, as in other vertebrates. Juan Fuentes showed that low Ca2+ diets lead to reduced body growth in length and weight in sturgeon Acipenser naccarii. However, the fish were able to partly compensate for the Ca2+ deficiency by increasing whole body Ca2+ uptake. PTHrP (1–34) increased plasma Ca2+ within 4 h through stimulation of Ca2+ influx and reduction of efflux. These observations support a role for PTHrP as a hypercalcemic factor in cartilaginous fish. PTHrP and parathyroid hormone (PTH) act via the same G-protein coupled receptors for which there are two in teleosts fish (PTH1R and PTH3R). Michael Greenwood cloned the two receptors in the euryhaline flounder, Platichthys flesus, and analysed the tissue expression in FW and SW adapted fish. Levels of PTH3R in the gills of FW-adapted flounder were 2-fold higher than in SW suggesting that this receptor may mediate the calcitropic action of PTHrP in this tissue. Selim Terhzaz provided a detailed account on the role of three new isoforms of the single Drosophila gene of Secretory Pathway Ca2+/Mn2+ ATPases (SPoCk), which are specific of the Golgi apparatus, peroxisomes and endoplasmic reticulum (ER). Overexpression of SPoCk isoforms strongly modify Ca2+ handling in isolated Drosophila cells and in the Malpighian tubule in vivo: the ER isoform influences IP3-mediated Ca2+ signalling; the Golgi isoform affects diuresis; whereas the peroxisome isoform colocalises with Ca2+ spherites and affects Ca2+storage and transport. The action of the three isoforms contributes to both Ca2+ bulk transport and storage, while simultaneously not affecting its signalling function.
Discussion
Endocrinology of calcium homeostasis Adelino Canario a, Gert Flik a b
b
Centre of Marine Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal Faculty of Science, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
Michelle Wheatly reviewed the role of binding proteins in the regulation of calcium homeostasis during periods of net vectorial influx using the crayfish, Procambarus clarkii, as a model. The proteins studied were the import and export proteins, epithelial Ca2+ channel (ECaC), sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), plasma membrane Ca2+ ATPase (PMCA) and Na+/Ca2+ exchanger (NCX). The expression of these proteins is a coordinated process at multiple levels including the apical vs. basolateral domains, plasma membranes vs. organelle membranes and transmembrane Ca2+ transporters and binding proteins. An integrative model of cellular Ca2+ homeostasis was presented which took into account the spatial and temporal protein expression during crayfish molting. Kristina Sundell presented a comparative account of Ca2+ regulation by vitamin D3 starting from the classical view that the vitamin D3 system evolved during the water to land transition in response to a scarcity of Ca2+ in the terrestrial environment. By comparing Ca2+ metabolism in freshwater (FW) and seawater (SW) fishes, it has been possible to establish conserved features, such as vitamin D3 metabolism and nuclear receptors, as well as rapid non-genomic divergent responses to 1,25(OH)2-vitamin D3 (calcitriol) and 24,25(OH)2-vitamin D3 mediated by membrane receptors, which appear to be dependent on Ca2+ availability. In the Free Communications Gert Flik showed that in the marine fish gilthead sea bream (Sparus aurata) only in conditions of Ca2+ deficiency in the water and in the diet, were plasma Ca2+ and parathyroid hormone-related protein (PTHrP) decreased. It was hypothesized that PTHrP may have a paracrine action to regulate branchial Ca2+ handling. Positive correlations between plasma PTHrP, calcium, phosphorus and magnesium may indicate a role
0016-6480/$ - see front matter Ó 2007 Published by Elsevier Inc. doi:10.1016/j.ygcen.2007.05.023
for the hormone in bone development. Finally, PTHrP potentiates estradiol-induced vitellogenesis in cultured hepatocytes hinting at a multiple role for the protein in fishes, as in other vertebrates. Juan Fuentes showed that low Ca2+ diets lead to reduced body growth in length and weight in sturgeon Acipenser naccarii. However, the fish were able to partly compensate for the Ca2+ deficiency by increasing whole body Ca2+ uptake. PTHrP (1–34) increased plasma Ca2+ within 4 h through stimulation of Ca2+ influx and reduction of efflux. These observations support a role for PTHrP as a hypercalcemic factor in cartilaginous fish. PTHrP and parathyroid hormone (PTH) act via the same G-protein coupled receptors for which there are two in teleosts fish (PTH1R and PTH3R). Michael Greenwood cloned the two receptors in the euryhaline flounder, Platichthys flesus, and analysed the tissue expression in FW and SW adapted fish. Levels of PTH3R in the gills of FW-adapted flounder were 2-fold higher than in SW suggesting that this receptor may mediate the calcitropic action of PTHrP in this tissue. Selim Terhzaz provided a detailed account on the role of three new isoforms of the single Drosophila gene of Secretory Pathway Ca2+/Mn2+ ATPases (SPoCk), which are specific of the Golgi apparatus, peroxisomes and endoplasmic reticulum (ER). Overexpression of SPoCk isoforms strongly modify Ca2+ handling in isolated Drosophila cells and in the Malpighian tubule in vivo: the ER isoform influences IP3-mediated Ca2+ signalling; the Golgi isoform affects diuresis; whereas the peroxisome isoform colocalises with Ca2+ spherites and affects Ca2+storage and transport. The action of the three isoforms contributes to both Ca2+ bulk transport and storage, while simultaneously not affecting its signalling function.