Accumulation and efflux of nickel from cultured pneumocytes.

The accumulation and efflux of nickel from three kinds of cultured pneumocytes were studied. Nickel rapidly penetrated the cells examined. The concentration of nickel in the cells was related to the volume of cytoplasm and surface area of the cells. Some metabolic inhibitors (NaN3, NaCN, NaAsO2) reduced the accumulation of nickel by up to 74%. Extracellular calcium regulated the accumulation of nickel into the cells. CaCl2 at 10 mM inhibited partially the accumulation of nickel, while nickel accumulation was enhanced in calcium free medium. From the efflux experiment, nickel was shown to be distributed to three different compartments in the cells, i.e., cell membrane, cytoplasm and intracellular constituents. Three rate constants were determined as k1 = 1.67-5.33, k2 = 0.031-0.037 and k3 = 0.002-0.007 min-1. These results suggest that cell membrane is readily permeable to nickel and that saturable nickel-binding sites might exist in the pneumocytes examined.