Patch electrode glass composition affects ion channel currents

The influence of patch electrode glass composition on macroscopic IV relations in inside-out patches of the cGMP-activated ion channel from rod photoreceptors was examined for a soda lime glass, a Kovar sealing glass, a borosilicate glass, and several soft lead glasses. In several glasses the shape or magnitude of the currents changed as the concentration of EGTA or EDTA was increased from 200 microM to 10 mM. The changes in IV response suggest that, at low concentrations of chelator, divalent cations are released from the electrode glass and interact with the cGMP-activated channel. Possible mechanisms are discussed to explain the observations, and several comments are made concerning the choice of a glass for patching.