Rat Kidney Cells in Primary Culture: Hormone-Mediated Desensitization of the Adenosine 3′,5′-Monophosphate Response to Parathyroid Hormone and Calcitonin*

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Abstract
To investigate the direct actions and the possible cellular mechanisms of parathyroid hormone (PTH) and salmon calcitonin (sCT) action in inducing the desensitization of renal cAMP responses to these hormones, we studied kidney cells in primary culture. Renal cells isolated from neonatal rats were cultured in F-12 medium plus 100 μl/ml calf serum. The cultured kidney cells reached confluent monolayer in 24 h and remained responsive to hormones, including PTH, sCT, vasopressin, and prostaglandin E1. Pretreatment of the cultured cells with PTH (2.5 × 10-7 M) or sCT (3 × 10-7 M) resulted in homologous desensitization in the cAMP responses to these hormones. Both PTH- and sCT-mediated desensitization were time and dose dependent. The EC505o for PTH-mediated desensitization was approximately 3.2 × 10-9 M, and that for sCT was 2.0 × 10-10 M. Cells that were desensitized to PTH or sCT showed normal responsiveness to cholera to×in, indicating that the catalytic and coupling units of the adenylate cyclase were not modified, suggesting that the locus for desensitization was at the receptor sites. We also found that the renal cell adenylate cyclase, after stimulation by PTH, was markedly different from that observed with sCT. The cAMP response to PTH was short-lived and readily reversible after removal of the hormone from the medium. Exposure to sCT resulted in stable activation of the adenylate cyclase system which was noted for several hours after the removal of sCT. sCT may form a stable complex with its receptors, thus activating the catalytic unit of the adenylate cyclase for a substantial period of time after removal of the hormone. This mechanism may account for the unique pharmacological efficacy of sCT.

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