TEA-sensitive potassium channels and inward rectification in regenerated rat sciatic nerve

Sucrose gap and intra-axonal recording techniques were used to identify the types of ion channels and inward rectification that are present in regenerated axons of adult (greater than 8 weeks) rat sciatic nerve after crush injury. In sucrose gap recordings, 4-aminopyridine (4-AP) led to slight broadening of the compound action potential (CAP) in normal nerve, and a greater broadening in regenerated nerves. By 12 days after sciatic nerve crush, regenerated nerves manifested an afterhyperpolarization (AHP) lasting up to 250 ms that was sensitive to tetraethylammonium (TEA). A similar TEA-sensitive AHP could be elicited with repetitive stimulation. Hyperpolarizing constant current steps (0.1 to 0.5 mA; 600-900 ms duration) applied across the sucrose gap through regenerated axons evoked membrane hyperpolarizations with a depolarizing, Cs(+)-sensitive relaxation in the response to hyperpolarization, which is characteristic of inward rectification, occurring after about 70 ms. The relaxation was present as early as 21 days after nerve crush. Intra-axonal recordings showed burst firing in 4-AP that was terminated by an AHP that temporally correlated with the TEA-sensitive AHP, and a relaxation in the response to hyperpolarizing current, similar to that of whole nerve recordings. The results demonstrate that in addition to voltage-sensitive sodium channels and 4-AP-sensitive potassium channels, there are TEA-sensitive and inwardly rectifying channels on mammalian regenerated peripheral nerve axons.