Single-channel properties of the reconstituted voltage-regulated Na channel isolated from the electroplax of Electrophorus electricus.

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Abstract
The tetrodotoxin-binding protein purified from electroplax of E. electricus was reincorporated into multilamellar vesicles that were used for patch recording. When excised patches of these reconstituted membranes were voltage clamped in the absence of neurotoxins, voltage-dependent single-channel currents were recorded. These displayed properties qualitatively and quantitatively similar to those reported for Na channels from nerve and muscle cells, including uniform single-channel conductances of the appropriate magnitude (.apprxeq. 11 pS in 95 mM Na+), mean open time of .apprxeq. 1.9 ms and 7-fold selectivity for Na+ over K+. Currents averaged from many depolarizations showed initial voltage-dependent activation and subsequent inactivation. In the presence of batrachotoxin, channels were observed with markedly different properties, including conductances of 20-25 pS (95 mM Na+), mean open times of .apprxeq. 28 ms, and no indication of inactivation. Evidently, the tetrodotoxin-binding protein of electroplax is a voltage-regulated Na channel.