Methylmercury mobilizes Ca++ from intracellular stores sensitive to inositol 1,4,5-trisphosphate in NG108-15 cells.

Fluorescence intensity was monitored from individual NG108-15 cells loaded with the Ca(++)-selective probe fura-2, and exposed to 2 microM methylmercury (MeHg). The initial effect of 2 microM MeHg was an elevation in intracellular Ca++ concentration ([Ca++]i), which was not blocked by lowering extracellular Ca++ (Ca++e), nifedipine (0.1 microM) or by Ni++ (1 mM). Addition of 100 microM Mn++ to Ca(++)-containing medium did not alter fluorescence intensity at either the Ca(++)-insensitive excitation wavelength of 360 nm or the Ca(++)-sensitive wavelength of 380 nm. Depolarization with K+ decreased the intensity at both wavelengths, indicating Mn++ entry. In the presence of Mn++, MeHg decreased the 380 nm, but not the 360 nm signal. Bradykinin (Bk) caused a transient increase in the fluorescence ratio, which was blocked by the endoplasmic reticulum Ca(++)-adenosine triphosphatase inhibitor thapsigargin. Pretreatment with Bk and thapsigargin reduced significantly the increase in ratio induced by MeHg from 21.9 +/- 3.4 to 6.9 +/- 1.8% of base line. Bk had no effect when applied after MeHg. Caffeine reduced the Bk-induced increase in [Ca++]i and the MeHg-induced increase in ratio from 21.9 +/- 3.4 to 9.0 +/- 2.1%. Thus, Bk, caffeine and MeHg all appear to release a common pool of intracellular calcium (Ca2+i). When applied after MeHg, Bk increased inositol 1,4,5-trisphosphate (IP3) by 305 +/- 27% compared to 270 +/- 29% in controls. Thus, MeHg did not induce Ca++ release by IP3 generation, nor did it block the effects of Bk by interfering with IP3 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)