Epidermal growth factor inhibits Na-Pi cotransport in weaned and suckling rats

In the present study, we determined the effect of epidermal growth factor (EGF; 10 mu g/100 g body wt) on sodium gradient-dependent phosphate transport (Na-P-i cotransport) regulation in suckling (12-day-old and weaned (24-day-old) rats. Weaned rats had higher proximal tubular brush border membrane vesicle (BBMV) Na-P-i cotransport activity (232 +/- 16 in weaned vs. 130 +/- 9 pmol.10 s(-1).mg protein(-1) in suckling rats, P < 0.05). Chronic treatment with EGF induced inhibition of BBMV Na-Pi cotransport in both suckling (130 +/- 9 vs. 104 +/- 7 pmol. 10 s(-1).mg protein(-1), P < 0.05) and weaned rats (232 +/-: 16 vs. 145 +/- 9 pmol.10 s(-1).mg protein(-1), P < 0.005). The inhibitory effect was selective for Na-P-i cotransport as there was no inhibition of Na-glucose cotransport. Weaned rats had a higher abundance of BBMV NaPi-2 protein than suckling rats (increase of 54%, P < 0.001) and a twofold increase in NaPi-2 mRNA. The EGF-induced inhibition of Na-P-i transport was paralleled by decreases in NaPi-2 protein abundance in bath weaned (decrease of 26%, P < 0.01) and suckling (decrease of 27%, P < 0.01) animals. In contrast, there were no changes in NaPi-2 mRNA abundance. We conclude that proximal tubule BBMV Na-P-i cotransport activity, NaPi-2 protein abundance, and NaPi-2 mRNA abundance are higher in weaned than in suckling rats. EGF inhibits Na-P-i cotransport activity in BB,SIV isolated from suckling and weaned rats, and this inhibition is mediated via a decrease in NaPi-2 protein abundance, in the absence of a change in NaPi-2 mRNA.