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First published online September 19, 2006
Journal of Experimental Biology 209, 3719-3728 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02436

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Dietary acidification enhances phosphorus digestibility but decreases H⁺/K⁺-ATPase expression in rainbow trout

Shozo H. Sugiura, Prabir K. Roy and Ronaldo P. Ferraris^*

Department of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA

View larger version (20K): [in a new window]   Fig. 1. Postprandial gastric luminal pH of fish and rats. The post-prandial hours (x axis) are in log scale (0 h is the pre-prandial value), and gastric luminal pH (y axis) is shown as mean ± s.e.m. (as error bars, N=8 for fish and N=4 for rats). Fish studied were four 2-month-old rainbow trout (10.24±0.54 g; mean body mass ± s.e.m.) and four 15-month-old rainbow trout (211.4±2.4 g). Since there was no significant difference between these small and mid-sized fish, they were pooled for statistical comparison with rats. Rats studied were four 1-2-month-old rats (120.3±3.2 g). Difference between fish and rats in gastric luminal pH at each postprandial hour is shown with asterisks: *P<0.05; **P<0.01. Gastric luminal pH of rats was much lower than that of fish at 1-6 h postprandial.

View larger version (29K): [in a new window]   Fig. 2. Phylogenic kinship of trout gastrin-like EST (A) and trout ATP4A-like EST (B) to those of other species. Based on the translated amino acid sequence, trout gastrin-like EST has 64% homology with halibut gastrin, and trout ATP4A-like EST is 98% homologous to flounder ATP4A. Gastrin and CCK belong to the same peptide family, but the trout gastrin-like EST belongs to a gastrin cluster that is sufficiently removed from the trout CCK cluster (not shown). Gas, gastrin; CCK: cholecystokinin; ATP4A: H+/K+-ATPase; ATP1A: Na+/K+-ATPase. Trout EST1 (gi:42752688) and trout EST2 (gi:42817423) in B are 97% homologous to one another in nucleotide base sequence.

View larger version (41K): [in a new window]   Fig. 3. Effects of various dietary acids (x axis) on relative gene expression (y axis) in the antral and corpus (body) regions of rainbow trout stomach. One of the following acids or antacid was added to the basal diet (No acid) (w/w). HCl: 12 mol 1-1 HCl 5.0%; H2SO4h, 18 mol l-1 H2SO4 3.5%; H2SO4L: 18 mol l-1 H2SO4 1.0%; acetic: glacial acetic acid 5.0%; antacid: CaCO3 5.0%. No acid: basal diet (see Table 1). Gray bars represent data of corpus stomach; white bars represent data of antral stomach. Each column represents the average (+ s.e.m. as error bar) of four fish. Columns within each stomach region labeled with different letters are significantly different (P<0.05). ATP4A, H+/K+-ATPase; SST, somatostatin; NBC, Na+/bicarbonate cotransporter). Differences of mRNA abundance between antral and corpus stomach (all treatments inclusive) were as follows: Gastrin-like gene (P=0.8); ATP4A (P=0.0003); SST1 (P=0.02); SST2 (P=0.002); SST2-2 (P=0.8); NBC (P=0.0007).

View larger version (14K): [in a new window]   Fig. 4. Correlation between ATP4A (H+/K+-ATPase, the proton pump) and NBC (Na+/bicarbonate cotransporter) mRNA abundance in the antral and corpus stomach of rainbow trout. Each dot represents one sample. One antral and one corpus sample was collected from each fish. In the antrum (open diamonds), ATP4A mRNA is nearly absent, whereas small amounts of NBC mRNA are present. In the corpus (filled diamonds), both ATP4A mRNA and NBC mRNA are abundant and their abundances are correlated to one another (regression of corpus ATP4A to corpus NBC: y=0.86x+0.36; R2=0.40). Units of x and y axes are relative (average of all data points is 1).

View larger version (15K): [in a new window]   Fig. 5. Dietary acidification increases phosphorus digestibility (A) but decreases H+/K+-ATPase mRNA expression (B) in rainbow trout. Each dot represents the mean (± s.e.m.) of six fish for phosphorus digestibility measurements, and four fish for H+/K+-ATPase mRNA measurements. Legend shows dietary treatments (acids used). Significance of dietary acidification on phosphorus digestibility (P<0.0001) and H+/K+-ATPase mRNA expression (P<0.0001) was evaluated by linear regression.