An early outward transient K+ current that depends on a preceding Na+ current and is enhanced by insulin.
A whole-cell early transient outward current occurs in rat myoballs if and only if there is an immediately preceding current of large amplitude through the voltage-gated, tetrodotoxin-inhibitable Na+ channel. This early outward transient is a K+ current, designated IK(Na+). Under the conditions in which IK(Na+) appears, simultaneous measurement of voltage and current, under voltage clamp, demonstrates that there is transient voltage escape to depolarized levels, peaking at about the time of peak inward Na+ current and resembling an action potential. IK(Na+) was never seen in the absence of this breach of the voltage clamp, suggesting that IK(Na+) might be an artefact due to transient depolarization from the clamp. However, when the voltage escape was mimicked by voltage commands under conditions in which the Na+ channel was not activated, there was no IK(Na). Insulin increased or produced IK(Na+) even though insulin had no effect on INa or on the delayed rectifier K+ current or on the escape from voltage clamp. It is concluded that there is a population of rat myoballs in which there is an early outward K+ current that requires an immediately preceding current through the voltage-gated, tetrodotoxin-inhibitable Na+ channel and is enhanced by insulin.
Zierler
K
K
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Wu
F S
FS
D000818:Animals; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology*; D006614:Hindlimb; D007328:Insulin / Q000494:pharmacology*; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000502:physiology*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
D007328:Insulin; D015222:Sodium Channels; D012964:Sodium; D011188:Potassium