PVP-containing solutions for analysis of divalent cation-dependent NMDA responses in Xenopus oocytes

The electrophysiological analysis of Ca(2+)-conducting ion channels in Xenopus oocytes is difficult due to secondary intracellular effects induced by Ca2+. In the presence of polyvinylpyrrolidone (PVP) membrane currents can be recorded in nominally divalent cation-free solutions. The Ca(2+)-permeable recombinant NMDA receptors of the NR1/NR2A subtype were used as assay system and the results show that PVP has no effect on NMDA receptor-induced currents. Ca2+ and Ba2+ depress NMDA-induced currents at submillimolar concentrations probably by interfering with the Na+/K+ flux. This block is fully reversible as also observed for Mg2+ but shows in contrast no pronounced voltage dependence. PVP-containing solutions may be useful for the analysis of divalent cation-dependent ion channels.