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

The amino-terminal fragment of a tumor parathyroid hormone-related peptide (PTHrP(1-34] produced by a human squamous cell carcinoma of the lung was recently synthesized. 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-sensitive 22Na 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.