Modulation of the ER Ca2+ channel BCC1 from tendrils of Bryonia dioica by divalent cations, protons and H2O2

Electrical properties of the ER Ca2+ channel BCC1 from tendrils of Bryonia dioica were analyzed after incorporation of BCC1 into black lipid bilayers. Single channel current fluctuations were modulated by divalent cations, protons and H2O2. Whereas the channel is permeable for Ca2+, Ba2+ and Sr2+, its conductance is strongly reduced in solutions containing MgCl2. Cu2+ and Zn2+ are potent inhibitors of BCC1 in micromolar concentrations. The open channel conductance of BCC1 increases with acidification of the electrolyte solution. H2O2 shows strong inhibitory effects on BCC1. The channel is almost completely closed at submillimolar concentrations of H2O2. The effects of pH and H2O2 on channel properties are directional and affect BCC1 at the Ca exit side, but not on the entry site. Thus, cytosolic pH and H2O2 levels may play an important role in the modulation of the cytoplasmic free calcium concentration through BCC1.