Effects of the level of mRNA expression on biophysical properties, sensitivity to neurotoxins, and regulation of the brain delayed-rectifier K+ channels Kv1.2.
Injection of 0.2 ng of cRNA encoding the brain Kv1.2 channel into Xenopus oocytes leads to the expression of a very slowly inactivating K+ current. Inactivation is absent in oocytes injected with 20 ng of cRNA although activation remains unchanged. Low cRNA concentrations generate a channel which is sensitive to dendrotoxin I (IC50 = 2 nM at 0.2 ng of cRNA/oocyte) and to less potent analogs of this toxin from Dendroaspis polylepis venom. A good correlation is found between blockade of the K+ current and binding of the different toxins to rat brain membranes. High cRNA concentrations generate another form of the K+ channel which is largely insensitive to dendrotoxin I (IC50 = 200 nM at 20 ng of cRNA per oocyte). At low cRNA concentrations, the expressed Kv1.2 channel is also blocked by other polypeptide toxins such as MCD peptide (IC50 = 20 nM), charybdotoxin (IC50 = 50 nM), and beta-bungarotoxin (IC50 = 50 nM), which bind to distinct and allosterically related sites on the channel protein. The pharmacologically distinct type of K+ channel expressed at high cRNA concentrations (20 ng of cRNA/oocyte) is nearly totally resistant to 100 nM MCD peptide and hardly altered by charybdotoxin and beta-bungarotoxin at concentrations as high as 1 microM. Both at low and at high cRNA concentrations, the expressed Kv1.2 channel is blocked by an increase in intracellular Ca2+ from the inositol trisphosphate sensitive pools and by the phorbol ester PMA that activates protein kinase C.
D000495:Allosteric Site; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D001923:Brain Chemistry; D003001:Cloning, Molecular; D004247:DNA; D009498:Neurotoxins / Q000633:toxicity*; D009865:Oocytes / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology; D012313:RNA / Q000378:metabolism; D018075:RNA, Complementary; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D014982:Xenopus laevis
D009498:Neurotoxins; D015221:Potassium Channels; D018075:RNA, Complementary; D012333:RNA, Messenger; D012313:RNA; D004247:DNA