Different types of K+ channel current are generated by different levels of a single mRNA.
A cloned human voltage-sensitive K+ channel HLK3 which is present in T-lymphocytes and in the brain was expressed in Xenopus oocytes and after permanent transfection of a human B-lymphocyte cell line (IM9). Injections of low cRNA concentrations into Xenopus oocytes led to the expression of a transient K+ current, with saturating current-voltage (I-V) relationship, which was abolished by repetitive stimulations due to a slow recovery from inactivation. This transient K+ channel current was fully inhibited by 10 nM charybdotoxin. Injection of high concentrations of the same RNA led to a non-inactivating K+ current, with linear I-V curve, which did not undergo use-dependent inactivation and was hardly sensitive to 10 nM charybdotoxin. Intermediate behaviour due to changing proportions of these two types of K+ channel expression were observed at intermediate RNA concentrations. Transient and non-inactivating K+ currents were also observed by both whole-cell and single channel patch-clamp recording from HLK3 transfected IM9 cells. The main conductance of the channel in the two different modes (inactivating and charybdotoxin-sensitive or non-inactivating and charybdotoxin-resistant) is the same (12-14 pS). Destruction of the cytoskeletal elements with cytochalasin D, colchicine or botulinum C2 toxin in oocyte experiments prevented expression of the sustained mode of the K+ channel. The results suggest that the sustained mode obtained at high RNA concentrations corresponds to channel clustering involving cytoskeletal elements. This differential functional expression of K+ channels associated with different levels of mRNA appears as a new important factor to explain the biophysical and pharmacological diversity of voltage-sensitive K+ channels.
Honoré
E
E
Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Valbonne, France.
Attali
B
B
Romey
G
G
Lesage
F
F
Barhanin
J
J
Lazdunski
M
M
D000818:Animals; D002460:Cell Line; D018999:Charybdotoxin; D006801:Humans; D015640:Ion Channel Gating; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012604:Scorpion Venoms / Q000494:pharmacology; D013601:T-Lymphocytes / Q000378:metabolism*; D014162:Transfection; D014982:Xenopus laevis
D015221:Potassium Channels; D012333:RNA, Messenger; D012604:Scorpion Venoms; D018999:Charybdotoxin