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).