Determining K+ channel activation curves from K+ channel currents.
Potassium ion channels are generally believed to have current-voltage (IV) relations which are linearly related to driving force ( V - E(K)), where V is membrane potential and E(K) is the potassium ion equilibrium potential. Consequently, activation curves for K+ channels have often been measured by normalizing voltage-clamp families of macroscopic K+ currents with (V - E(K)), where V is the potential of each successive step in the voltage clamp sequence. However, the IV relation for many types of K+ channels actually has a non-linear dependence upon driving force which is well described by the Goldman-Hodgkin-Katz relation. When the GHK dependence on (V - E(K)) is used in the normalization procedure, a very different voltage dependence of the activation curve is obtained which may more accurately reflect this feature of channel gating. Novel insights into the voltage dependence of the rapidly inactivating I(A) channels Kv1.4 and Kv4.2 have been obtained when this procedure was applied to recently published results.
Clay
J R
JR
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. jrclay@helix.nih.gov
D000818:Animals; D002460:Cell Line; D005260:Female; D006801:Humans; D051665:Kv1.4 Potassium Channel; D008564:Membrane Potentials / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D011994:Recombinant Proteins / Q000378:metabolism; D051672:Shal Potassium Channels; D014982:Xenopus laevis
C496977:KCNA4 protein, human; C497018:KCND2 protein, human; D051665:Kv1.4 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011994:Recombinant Proteins; D051672:Shal Potassium Channels