We used the patch-clamp technique to identify and characterize the electrophysiological, biophysical, and pharmacological properties of K+ channels in enzymatically dissociated ventricular cells of the land pulmonate snail Helix. The family of outward K+ currents started to activate at −30 mV and the activation was faster at more depolarized potentials (time constants: at 0 mV 17.4 ± 1.2 ms vs. 2.5 ± 0.1 ms at + 60 mV). The current waveforms were similar to those of the A-type family of voltage-dependent K+ currents encoded by Kv4.2 in mammals. Inactivation of the current was relatively fast, i.e., 50.2 ± 1.8% of current was inactivated within 250 ms at + 40 mV. The recovery of K+ channels from inactivation was relatively slow with a mean time constant of 1.7 ± 0.2 s. Closer examination of steady-state inactivation kinetics revealed that the voltage dependency of inactivation was U-shaped, exhibiting less inactivation at more depolarized membrane potentials. On the basis of this phenomenon, we suggest that a channel encoded by Kv2.1 similar to that in mammals does exist in land pulmonates of the Helix genus. Outward currents were sensitive to 4-aminopyridine and tetraethylammonium chloride. The last compound was most effective, with an IC 50 of 336 ± 142 µmol l−1. Thus, using distinct pharmacological and biophysical tools we identified different types of voltage-gated K+ channels.
The Journal of Membrane Biology – Springer Journals
Published: Jan 1, 2004
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