Functional expression of the rat heart I Na+ channel isoform. Demonstration of properties characteristic of native cardiac Na+ channels.

We describe the expression of functional Na+ channels in Xenopus oocytes injected with cRNA transcribed from the rat heart I cDNA clone. The expressed rat heart I Na+ currents show kinetic properties and resistance to tetrodotoxin and saxitoxin which are characteristic of native cardiac Na+ currents. The primary amino acid sequence of the rat heart I alpha-subunit is therefore sufficient for expression of tetrodotoxin resistance, and the rat heart I clone is likely to account for the tetrodotoxin-resistant phenotype of cardiac and denervated skeletal muscle.