Cellular metabolism of lead: a kinetic analysis in cultured osteoclastic bone cells

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 intoxication. The metabolism of lead in osseous tissue is also clinically important because it is the major site of chelation by therapeutic agents, such as CaNa2-EDTA and D-penicillamine. Experiments were conducted to characterize the steady-state kinetic distribution and behavior of 210Pb in osteoclastic bone cells 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 microM 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 approximately 10% (S1). Approximately 12% (S2), and approximately 78% (S3) of total cellular lead (1.2 nmol/mg cell protein). The halftimes for isotopic exchange were 1, 27, and 480 min, respectively. These data indicate that lead is readily exchangeable from osteoclastic bone cells and, as in soft tissues (hepatocytes), the bulk of cellular lead is associated with mitochondria.