The effects of tris(hydroxymethyl)aminomethane and calcium ionophores on the biosynthesis of proparathormone and the formation and degradation of parathormone in bovine parathyroid tissue

Abstract

A comparative study of ultrastructural and biochemical effects of Tris and ionophores X537A and A23187 on bovine parathyroid tissue is presented. When parathyroid slices were incubated with 3H-leucine and 3H-lysine for 10 minutes alone or with Tris (50 mM), A23187 (9.5-19 microM) or X537A (8.5-17 microM), the incorporation of the amino acids into radioactive proparathormone (proPTH) was similar, indicating that biosynthesis of the hormone was not affected. After 120 minutes of incubation, however, Tris inhibited the conversion of proPTH to parathormone (PTH), judged by a decrease in cellular and secreted radioactive PTH and a corresponding increase in radioactive cellular proPTH. These changes were accompanied by marked dilatation of Golgi membranes. With both concentrations of A23187 and the low concentration of X537A there were no changes in amounts of radioactive proPTH, moderate decreases in cellular and secreted radioactive PTH, and little discernible distension of the Golgi membranes. At 17 microM X537A there was moderate increase in amount of radioactive proPTH, a marked decrease in amount of radioactive PTH and swelling of the Golgi membranes. Taken together, these findings suggest that Tris inhibited conversion of proPTH to PTH by disrupting the Golgi zone-the site of conversion of proPTH to PTH; that A23187 and the low concentration of X537A decreased production of PTH by enhancing its degradation; and that X537A at the higher concentration acted both by inhibiting conversion of proPTH to PTH and by enhancing the degradation of PTH.