Endocrinology, Vol 129, 1463-1470, Copyright © 1991 by Endocrine Society

ARTICLES

Thrombin and parathyroid hormone mobilize intracellular calcium in rat osteosarcoma cells by distinct pathways

M Babich, H Choi, RM Johnson, KL King, GE Alford and RA Nissenson
Endocrine Section, Veterans Affairs Medical Center, San Francisco, California 94121.

The mechanisms by which PTH and thrombin mobilize intracellular Ca2+ (Cai2+) were examined in UMR 106-H5 rat osteosarcoma cells. Bovine PTH- (1-34) (24 pM to 240 nM) produced a dose-dependent increase in Cai2+ (EC50, 3 nM), which returned to baseline within 75 sec. Human alpha- thrombin produced an increase in Cai2+ (ECmax, 10 U/ml) which was similar to that of PTH with respect to both magnitude and time course. Chelation of extracellular calcium with 5.0 mM EGTA did not alter the Cai2+ response to either PTH or thrombin. When added together at maximally effective concentrations, PTH and thrombin produced additive effects on Cai2+ in the presence and absence of EGTA. The additive effects of PTH and thrombin on Cai2+ were confirmed at the single cell level, using laser-based image analysis. Bradykinin (1 microM) produced a significant increase in Cai2+ in UMR 106-H5 cells which was of lesser magnitude than the peak 2- to 3-fold increase elicited by PTH or thrombin. Preexposure of cells to 10 U/ml thrombin for 2 min abolished the Cai2+ response to bradykinin, whereas preexposure to 240 nM PTH had no effect on the Cai2+ response to bradykinin. Thrombin elicited a rapid increase in the accumulation of 3H-labeled inositol phosphates (IP2 and IP3) in UMR 106-H5 cells, with increases in [3H]1,4,5-IP3 detectable as early as 15 sec after the addition of thrombin. Bradykinin increased [3H]IP production to a lesser extent than thrombin, whereas PTH neither increased [3H]IP accumulation nor potentiated the [3H]IP response to thrombin. The results suggest that thrombin and bradykinin mobilize Cai2+ from a shared IP3-responsive calcium pool, whereas PTH may use signals in addition to 1,4,5-IP3 to mobilize calcium from a distinct cellular calcium pool. Alternatively, specific calcium compartmentalization exists, and there is differential coupling of these agonists to the 1,4,5-IP3/Cai2+ pathway.

This article has been cited by other articles:

				A. D. Short and C. W. Taylor Parathyroid Hormone Controls the Size of the Intracellular Ca2+ Stores Available to Receptors Linked to Inositol Trisphosphate Formation J. Biol. Chem., January 21, 2000; 275(3): 1807 - 1813. [Abstract] [Full Text] [PDF]

				R. S. Mathias, K. Mikoshiba, T. Michikawa, A. Miyawaki, and H. E. Ives IP3 receptor blockade fails to prevent intracellular Ca2+ release by ET-1 and alpha -thrombin Am J Physiol Cell Physiol, June 1, 1998; 274(6): C1456 - C1465. [Abstract] [Full Text] [PDF]

				A.-S. Jobert, C. Leroy, D. Butlen, and C. Silve Parathyroid Hormone-Induced Calcium Release from Intracellular Stores in a Human Kidney Cell Line in the Absence of Stimulation of Cyclic Adenosine 3',5'-Monophosphate Production Endocrinology, December 1, 1997; 138(12): 5282 - 5292. [Abstract] [Full Text] [PDF]

				N. R. Jorgensen, S. T. Geist, R. Civitelli, and T. H. Steinberg ATP- and Gap Junction-dependent Intercellular Calcium Signaling in Osteoblastic Cells J. Cell Biol., October 20, 1997; 139(2): 497 - 506. [Abstract] [Full Text] [PDF]

				X. Xu, W. Zeng, and S. Muallem Regulation of the Inositol 1,4,5-Trisphosphate-activated Ca[IMAGE] Channel by Activation of G Proteins J. Biol. Chem., May 17, 1996; 271(20): 11737 - 11744. [Abstract] [Full Text] [PDF]

				Y. Tong, J. Zull, and L. Yu Functional Expression and Signaling Properties of Cloned Human Parathyroid Hormone Receptor in Xenopus Oocytes J. Biol. Chem., April 5, 1996; 271(14): 8183 - 8191. [Abstract] [Full Text] [PDF]