K+ channels in cardiomyocytes of the pulmonate snail helix.
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 micro mol l(-1). Thus, using distinct pharmacological and biophysical tools we identified different types of voltage-gated K(+) channels.
Kodirov
S A
SA
Department of Cardiology, Medical University Hospital Heidelberg, 69120 Heidelberg, Germany. skodirov@hms.harvard.edu
Zhuravlev
V L
VL
Pavlenko
V K
VK
Safonova
T A
TA
Brachmann
J
J
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006352:Heart Ventricles / Q000187:drug effects; D006372:Helix, Snails / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium / Q000494:pharmacology; D016276:Ventricular Function
D015220:Calcium Channels; D015221:Potassium Channels; D019789:Tetraethylammonium; D015761:4-Aminopyridine