EFFECTS OF LEAD, MERCURY, AND METHYL MERCURY ON GAP-JUNCTIONS AND [CA2-CELLS(](I) IN BONE)

Heavy metals such as lead (Pb), mercury (Hg), and methyl mercury (MeHg ) impair cell functions. For bone it is known that Pb changes bone for mation rates, which depend on intracellular free calcium concentration ([Ca2+](i)). Since heavy metals compete with Ca at multiple sites and increased [Ca2+](i) reduces gap junctional coupling between bone cell s, we analyzed the effects of extracellular (e) and intracellular (i) application of Pb. Hg, and MeHg on these channels. Using primary cultu res of osteoblast-like cells, relative changes of [Ca2+], were studied in Fura-YAM loaded cells. Parallel intracellular recordings of neighb oring cells were obtained using a conventional and a patch electrode. Pb-(e) (5 mu mo/liter; n = 3) and Hg-(e) (5 mu mol/liter; n = 3) as we ll as Pb-(i) (25 mu mol/liter; n = 7) did not change the coupling (Del ta MP2/Delta MP1). In contrast, MeHg(e) (1-10 mu mol/liter; n = 6) and Hg-(i) (greater than or equal to 5 mu mol/liter; n = 8) reduced the c oupling to 79.5 +/- 19.3% and 62.4 +/- 15.3%, respectively, within 15- 20 minutes. The reduction of coupling followed individual time courses , and in no case was a steady state of decoupling reached within 20 mi nutes. Extracellular application of Pb-(e) (5 mu mol/liter, n = 74) fo r 20 minutes, linearly elevated the Fura emission ratio reflecting tra nsmembrane Pb permeation rather than [Ca2+]i increase. Hg-(e)(n = 48) slightly increased [Ca2+], from 100 to less than or equal to 200 nmol/ liter, whereas MeHg(e) (5 mu mol/liter, n = 52) released Ca2+ from int ernal stores, thus increasing [Ca2+]i up to 2 mu mol/liter. In conclus ion, Pb-(e), Pb-(i) and Hg-(e) do and not affect gap junctional coupli ng per se. Since MeHg(e) Hg-(i) deplete calcium stores, the decrease o f the electric coupling is attributable to increased [Ca2+](i), which affects gap junction channels.