Patch clamp characterization of a non-selective cation channel of ER membranes purified from Beta vulgaris taproots.

The ER fraction from red beet taproot was purified on sucrose gradient and giant liposomes, suitable for patch clamping, were formed by dehydration-rehydration of the lipid film. Single-channel recordings on excised and attached patches revealed a large conductance (165 pS) cation (P(Cl-)/P(K+) < 0.03) channel with equal conductance and relative permeability for Na+ and K+. This non-selective cation channel was also highly permeable for Ca2+. We failed to detect any single-channel currents activated by a direct application of d-myo-inositol 1,4,5 trisphosphate, despite the fact that the ER membranes were native.