Effects of inorganic mercury (Hg2+) on calcium channel currents and catecholamine release from bovine chromaffin cells

Abstract

The effects of inorganic mercury (Hg2+) on calcium channel currents and the potassium-evoked catecholamine release of bovine chromaffin cells in culture were examined. The effects of cadmium (Cd2+), known to block calcium channels and reduce catecholamine release of chromaffin cells, were studied for comparison. Calcium channel currents were recorded in the whole-cell configuration of the patch-clamp technique. Hg2+ is a potent calcium channel blocker in bovine chromaffin cells. The IC50 value is about 3 microM, the Hill slope 1.46. In a concentration of 100 microM, Hg2+ blocked the currents completely; 100 microM Cd2+ had the same effect. Potassium-evoked catecholamine release from chromaffin cells was measured at different time-points with high-performance-liquid-chromatography (HPLC) under control conditions and in the presence of different Hg2+ concentrations. Low Hg2+ concentrations (0.1 and 1 microM) did not affect the amount of the catecholamines epinephrine (E) and norepinephrine (NE) which was released. Under identical conditions 1 microM Cd2+ also had no effect on release. With 10 microM Hg2+ there was a time-dependent increase in the potassium-evoked catecholamine release (by 27% after 8 min). The E/NE ratio was not altered, suggesting that the release of both hormones was increased similarly. In contrast to this, the release was slightly reduced with 10 microM Cd2+. In the presence of 100 microM Hg2+, there was a reduction of the release during an early phase, followed by an increase. The reduction is most probably due to the fast and effective calcium channel block by Hg2+ in this high concentration.(ABSTRACT TRUNCATED AT 250 WORDS)