Viral vector-mediated expression of K+ channels regulates electrical excitability in skeletal muscle

Modification of K+ currents by exogenous gene expression may lead to therap eutic interventions in skeletal muscle diseases characterized by alteration s in electrical excitability. In order to study the specific effects of inc reasing outward K+ currents, we expressed a modified voltage-dependent K+ c hannel in primary cultured rat skeletal muscle cells. The rat Kv1.4 channel was expressed as an N-terminal fusion protein containing a bioluminescent marker (green fluorescent protein). Transgene expression was carried out us ing the helper-dependent herpes simplex 1 amplicon system. Transduced myoba lls, identified using fluorescein optics and stud-led electrophysiologicall y with single-cell patch clamp, exhibited a greater than two-fold increase in K+ conductance by 20-30 h after infection. This increase in K+ current l ed to a decrease in membrane resistance and a 10-fold increase in the curre nt threshold for action potential generation. Electrical hyperexcitability induced by the Na+ channel toxin anemone toxin II (1 mum) was effectively c ounteracted by overexpression of Kv1.4 at 30-32 h after transduction. Thus, virally induced overexpression of a voltage-gated K+ channel in skeletal m uscle has a powerful effect in reducing electrical excitability.