Tumoral synthetic parathyroid hormone related peptide inhibits amiloride-sensitive sodium transport in cultured renal epithelia

The amino-terminal fragment of a tumoral parathyroid hormone-related peptide (PTHrP (1–34)) produced by a human squamous cell carcinoma of the lung was recently synthetized. In the present work its effect on the amiloride-sensitive sodium transport, taken as an estimate of the Na⁺/H⁺ exchanger activity of cultured opossum kidney (OK) epithelia was compared to that of synthetic bovine parathyroid hormone (bPTH (1–34)). Both PTHrP (1–34) and bPTH (1–34) inhibited the initial rate of amiloride-sensitive²²Na transport. Half maximal inhibitory activity was obtained at about 10^–11 M for both PTHrP (1–34) and bPTH (1–34). In conclusion, tumoral PTHrP (1–34) appears to be as effective as bPTH (1–34) for inhibiting the amiloride-sensitive Na transport, and presumably for decreasing the activity of the Na⁺/H⁺ exchanger present in the apical membrane of kidney epithelial cells.