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Selective Proteolysis of the Receptor for Parathyroid Hormone in Renal Corte¹

Metabolism Division, Department of Medicine, Washington University School of Medicine St. Louis, Missouri 63110

Abstract

Studies were carried out to determine if the receptors for parathyroid hormone, calcitonin, and prostaglandin E₁ could be differentiated in renal cortex. Slices of rabbit renal cortex were incubated in buffer containing theophylline for 1 hr and then in fresh buffer with and without hormone for an additional period of 15 to 30 min. Parathyroid hormone caused a marked increase in 3',5'-AMP in both the tissue and the reaction medium. The maximal increase in 3',5'-AMP in response to prostaglandin Ej was similar to that of parathyroid hormone in the tissue but significantly less in the medium. The maximal response to calcitonin was less in both the tissue and the medium. Addition of 200 µg/ml trypsin to the first incubation abolished the subsequent response to parathyroid hormone in both the tissue and the reaction medium, but did not affect the basal concentration of 3',5'-AMP or the response to calcitonin or prostaglandin E₁. Controls were carried out to show that the lack of response to parathyroid hormone could not be attributed to hydrolysis of the hormone by residual trypsin. Slices were also homogenized after preincubation with and without trypsin and assayed for adenylate cyclase activity. Incubation with trypsin markedly diminished the increase in enzyme activity in response to parathyroid hormone but did not alter the basal activity or the response to calcitonin or sodium fluoride. The response to prostaglandin Ei was significantly increased. Combinations of any two or the three hormones at maximal concentrations caused an additive increase in adenylate cyclase activity. The results indicate that the receptors for parathyroid hormone, calcitonin and prostaglandin E₁ in renal cortex are separate and the receptor for parathyroid hormone can be selectively hydrolyzed by proteolytic digestion. (Endocrinology 96: 70, 1975)

Footnotes

¹ Supported by USPHS Grant RO1 AM16926.

² Investigator, Howard Hughes Medical Institute.

Received April 3, 1974.