SKCa channels mediate the medium but not the slow calcium-activated afterhyperpolarization in cortical neurons.
Many neurons, including pyramidal cells of the cortex, express a slow afterhyperpolarization (sAHP) that regulates their firing. Although initial findings suggested that the current underlying the sAHP could be carried through SK(Ca) channels, recent work has uncovered anomalies that are not congruent with this idea. Here, we used overexpression and dominant-negative strategies to assess the involvement of SK(Ca) channels in mediating the current underlying the sAHP in pyramidal cells of the cerebral cortex. Pyramidal cells of layer V exhibit robust AHP currents composed of two kinetically and pharmacologically distinguishable currents known as the medium AHP current (I(mAHP)) and the slow AHP current (I(sAHP)). I(mAHP) is blocked by the SK(Ca) channel blockers apamin and bicuculline, whereas I(sAHP) is resistant to these agents but is inhibited by activation of muscarinic receptors. To test for a role for SK(Ca) channels, we overexpressed K(Ca)2.1 (SK1) and K(Ca)2.2 (SK2), the predominant SK(Ca) subunits expressed in the cortex, in pyramidal cells of cultured brain slices. Overexpression of K(Ca)2.1 and K(Ca)2.2 resulted in a fourfold to fivefold increase in the amplitude of I(mAHP) but had no detectable effect on I(sAHP). As an additional test, we examined I(sAHP) in a transgenic mouse expressing a truncated SK(Ca) subunit (SK3-1B) capable of acting as a dominant negative for the entire family of SK(Ca)-IK(Ca) channels. Expression of SK3-1B profoundly inhibited I(mAHP) but again had no discernable effect on I(sAHP). These results are inconsistent with the proposal that SK(Ca) channels mediate I(sAHP) in pyramidal cells and indicate that a different potassium channel mediates this current.
Villalobos
Claudio
C
Department of Psychiatry and Behavioral Neuroscience, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Shakkottai
Vikram G
VG
Chandy
K George
KG
Michelhaugh
Sharon K
SK
Andrade
Rodrigo
R
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D005625:Frontal Lobe / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D015870:Gene Expression; D049452:Green Fluorescent Proteins; D006801:Humans; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017966:Pyramidal Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013003:Somatosensory Cortex / Q000166:cytology / Q000378:metabolism / Q000502:physiology
C496894:KCNN1 protein, human; C496897:KCNN2 protein, human; C496895:Kcnn1 protein, mouse; C496896:Kcnn1 protein, rat; C496898:Kcnn2 protein, mouse; C496899:Kcnn2 protein, rat; C496900:Kcnn3 protein, mouse; C496901:Kcnn3 protein, rat; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008164:Luminescent Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D051640:Small-Conductance Calcium-Activated Potassium Channels; D049452:Green Fluorescent Proteins; D002118:Calcium