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First published online August 30, 2006
Journal of Experimental Biology 209, 3550-3557 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02399
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PTHrP regulation and calcium balance in sea bream (Sparus auratus L.) under calcium constraint

Wout Abbink1, Gideon S. Bevelander1, Xiaoming Hang2, Weiqun Lu2, Pedro M. Guerreiro3, Tom Spanings1, Adelino V. M. Canario3 and Gert Flik1,*

1 Department of Animal Physiology, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
2 Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
3 CCMAR, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal


Figure 1
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  		Fig. 1. (A) Gill calcium influx (FinCa2+; N=10) and (B) drinking rate (DR; N=10) significantly decreased in fish exposed to diluted seawater (DSW) for 30 days. The four groups of fish are: group a, control (34{per thousand} salinity, Ca+ diet) and three test groups: group b (34{per thousand} salinity, Cadiet), group c (2.5{per thousand} salinity, Ca+ diet) and group d (2.5{per thousand} salinity, Cadiet). Asterisks indicate significant difference (P<0.01) compared with control values. Values are means ± s.d.

 

Figure 2
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  		Fig. 2. (A) Plasma calcium levels (N=7 for the short-term experiment and N=10 for the long-term experiment) show the strict control of the ionic fraction, which only slightly, but significantly decreased after long-term calcium constraint in both water and diet. (B) In accordance, plasma sPTHrP decreased significantly in group d compared to controls. Asterisks indicate significant difference (P<0.05) from control group a. Values are means ± s.d. SW, full strength seawater; DSW, diluted seawater.

 

Figure 3
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  		Fig. 3. Positive relationships were found between plasma sPTHrP and (A) plasma ionic calcium (linear regression; R2=0.30, N=39, P<0.05) and between plasma sPTHrP and (B) the body mass of the fish (power function; R2=0.37, N=148, P<0.001).

 

Figure 4
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  		Fig. 4. Immunostaining for (1-34)sPTHrP (A) and somatolactin (SL; B) in sea bream pituitary glands shows the co-localisation for sPTHrP and SL in cells of the pars intermedia, bordering the pars nervosa (pn). Magnification, 400x. Controls with omission of the first antibody and pre-absorption with sPTHrP confirmed the specificity of sPTHrP immunoreactivity.

 

Figure 5
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  		Fig. 5. Expression of pthrp, pth1r and casr mRNA (N=7) in the pituitary gland is downregulated in fish after 3 h of exposure to diluted seawater (DSW), whereas no effect was found in gill tissue. Asterisks indicate significant difference (P<0.05) compared with full strength seawater (SW) values. Values are means ± s.d.

 

Figure 6
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  		Fig. 6. Expression of pthrp, pth1r and casr mRNAs (N=10) is significantly downregulated in pituitary gland (A) in the fish exposed to low calcium in dilute seawater for 30 days, whereas gill tissue (B) shows a significant upregulation of pthrp and pth1r mRNAs under these conditions. Asterisks indicate significant difference (P<0.05) compared with the controls (group a). Values are means ± s.d.

 

Figure 7
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  		Fig. 7. In the short-term experiment, a negative correlation between pituitary gland pthrp expression and plasma Ca2+ was found in fish exposed to full strength seawater (SW) (R2=0.71; N=7; P<0.01). In fish exposed to diluted seawater (DSW), no significant relationship was found. No such data were available for the long-term experiment.

 

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© The Company of Biologists Ltd 2006