Hormonal Responsiveness of Adenylate Cyclase Activity from Separated Bone Cells

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Abstract
This study examines the in vitro hormonal responsiveness of adenylate cyclase activity prepared from different types of bone cells. Adult rat skeletal tissue was separated into four cell populations: periosteum, osteoblasts, osteocytes, and mixed marrow cells. Particulate fractions (2200 x g) prepared from each of the bone cell populations were assayed for adenylate cyclase activity following the procedures of Marcus and Aurbach (6). A linear dose response curve was observed when adenylate cyclase activity from osteoblasts and osteocytes was plotted vs die log dose of parathyroid hormone (PTH) (0.5-15 U/70 μl). The maximum increases in activity were 2- to 4-fold. A dose-related response curve was also observed when activity from these same two cell types was plotted vs the log dose of thyrocalcitonin (TCT) (0.01–0.5 MRC U/70 μl). The maximum increase was 1.8 times control level. The response to TCT was only found consistently when EGTA was added to the assay media. Enzyme preparations from periosteum and marrow cells did not respond to either PTH or TCT. Glucagon and prostaglandin E1, increased enzyme activity prepared from osteocytes but not osteoblasts. Epinephrine, somatotrophin, triiodothyronine, prostaglandins E2, Flo and F2α did not stimulate enzyme act vity in either osteoblasts or osteocytes. The addition of TCT did not significantly affect PTH-stimulated activity in osteoblasts but had an additive effect to PTH-stimulated activity in osteocytes. Thus, this study provides evidence that two types of bone cells, osteoblasts and osteocytes, contain adenylate cyclase responsive to PTH and TCT. The evidence also demonstrates that TCT responsiveness is enhanced with EGTA. (Endocrinology95: 130, 1974

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