Quantitative interactions between Pb2+ and Ca2+ homeostasis in cultured osteoclastic bone cells.
Cellular calcium homeostasis and calcium-mediated cell functions are conceptually attractive processes to be involved in the manifestation(s) of lead toxicity including impaired skeletal growth and cardiovascular and neurological dysfunction. Knowledge of Ca:Pb and Pb:Ca ratios in different structural and functional compartments of cells is essential for identifying, characterizing, and understanding the significance of Pb2+-Ca2+ interactions. Experiments were conducted to characterize the steady-state kinetic distribution and behavior of 45Ca in primary cultures of murine osteoclastic bone cells. Bone cells, derived from mouse calvaria, were enriched for osteoclasts by a sequential collagenase digestion and maintained in primary culture for 1 week. Cultures were labeled with 45Ca for two or 24 hr and the kinetic parameters were obtained by analysis of 45Ca washout curves. Cellular metabolism was based upon a model with three kinetic pools of intracellular Ca2+ containing approximately 45, 25, and 30% of the total cell calcium. In addition, we describe quantitative measurements of Ca:Pb and Pb:Ca ratios at important functional cell sites of Ca2+ transport and storage in intact cells. The intracellular relationships of Ca2+ and Pb2+ were calculated concurrently in individual cultures, using kinetic analysis of dual-label 45Ca and 203Pb washout curves. The Ca:Pb ratios of the rate constants and half-times were approximately 1:1, supporting the concept of similar cellular metabolism of the two elements. The Ca:Pb ratios for the kinetic pools and fluxes were considerably higher than 1:1. These in situ Ca:Pb relationships should be useful for designing and evaluating Ca-Pb studies with calmodulin, isolated mitochondria, and other individual components of the calcium messenger system. Moreover, these data demonstrate both similarities and differences in the kinetic distribution and behavior of Ca2+ and Pb2+ in osteoclastic bone cells.
Rosen
J F
JF
Department of Pediatrics, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, New York 10467.
Pounds
J G
JG
D000818:Animals; D002116:Calcitonin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D006706:Homeostasis; D007854:Lead / Q000378:metabolism*; D051379:Mice; D010010:Osteoclasts / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology
D010281:Parathyroid Hormone; D007854:Lead; D002116:Calcitonin; D002118:Calcium