MODULATION OF THE ER CA2-DIOICA BY DIVALENT-CATIONS, PROTONS AND H2O2( CHANNEL BCC1 FROM TENDRILS OF BRYONIA)

Electrical properties of the ER Ca2+ channel BCC1 from tendrils of Bry onia dioica were analyzed after incorporation of BCC1 into black lipid bilayers, Single channel current fluctuations were modulated by dival ent cations, protons and H2O2, Whereas the channel is permeable for Ca 2+, Ba2+ and Sr2+, its conductance is strongly reduced in solutions co ntaining MgCl2, Cu2+ and Zn2+ are potent inhibitors of BCC1 in micromo lar concentrations, The open channel conductance of BCC1 increases wit h acidification of the electrolyte solution, H2O2 shows strong inhibit ory effects on BCC1, The channel is almost completely closed at submil limolar concentrations of H2O2. The effects of pH and H2O2 on channel properties are directional and affect BCC1 at the Ca exit side, but no t on the entry site, Thus, cytosolic pH and H2O2 levels may play an im portant role in the modulation of the cytoplasmic free calcium concent ration through BCC1. (C) 1997 Federation of European Biochemical Socie ties.