1249 CELLULAR METABOLISM OF LEAD: A KINETIC ANALYSIS IN CULTURED OSTEOCLASTIC BONE CELLS

Abstract

Detailed characterization of the modulation of lead metabolism in bone is necessary to understand the role of skeletal lead in the expression of clinical and biochemical effects of lead. The metabolism of lead in osseous tissue is also important clinically because it is the major site of chelation by therapeutic agents, such as CaNa₂EDTA and d-penicillamine. Experiments were conducted to characterize the steady-state kinetic distribution and behavior of ²¹⁰pb, and to identify the biological structures or functions associated with the kinetic pools. 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 ²¹⁰pb as 5 μM lead acetate for 20 hr and the kinetic parameters were obtained by analysis of ²¹⁰pb washout curves. Cellular metabolism was defined by three kinetic pools of intracellular lead containing ∼10% (Sl), ∼15% (S₂) and ∼757. (S₃) of total cellular lead (1.7-2.2 nmol/mg cell protein). The halftimes for isotopic exchange were 1, 40 and 1000 minutes, respectively. Less than one half of S₁ was labile to chelation by EGTA and thus defined as extracellular. KCN, DNP and DBcAMP decreased S₃, whereas increasing medium PO₄ to 4 mM increased S₃, thereby suggesting that S₃ includes mitochondrial ²¹⁰Pb. These data indicate that lead is readily mobilized from osteoclastic bone cells and, like soft tissues (hepatocytes), the bulk of cellular lead is associated with mitochondria.

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