Epidermal growth factor inhibits Na-Picotransport in weaned and suckling rats

Abstract

In the present study, we determined the effect of epidermal growth factor (EGF; 10 μg/100 g body wt) on sodium gradient-dependent phosphate transport (Na-P_icotransport) 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_icotransport activity (232 ± 16 in weaned vs. 130 ± 9 pmol ⋅ 10 s⁻¹⋅ mg protein⁻¹in suckling rats, P < 0.05). Chronic treatment with EGF induced inhibition of BBMV Na-P_icotransport 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_icotransport 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_itransport was paralleled by decreases in NaPi-2 protein abundance in both 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_icotransport activity, NaPi-2 protein abundance, and NaPi-2 mRNA abundance are higher in weaned than in suckling rats. EGF inhibits Na-P_icotransport activity in BBMV 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.