Large-conductance calcium-activated potassium channels in purkinje cell plasma membranes are clustered at sites of hypolemmal microdomains.
Calcium-activated potassium channels have been shown to be critically involved in neuronal function, but an elucidation of their detailed roles awaits identification of the microdomains where they are located. This study was undertaken to unravel the precise subcellular distribution of the large-conductance calcium-activated potassium channels (called BK, KCa1.1, or Slo1) in the somatodendritic compartment of cerebellar Purkinje cells by means of postembedding immunogold cytochemistry and SDS-digested freeze-fracture replica labeling (SDS-FRL). We found BK channels to be unevenly distributed over the Purkinje cell plasma membrane. At distal dendritic compartments, BK channels were scattered over the plasma membrane of dendritic shafts and spines but absent from postsynaptic densities. At the soma and proximal dendrites, BK channels formed two distinct pools. One pool was scattered over the plasma membrane, whereas the other pool was clustered in plasma membrane domains overlying subsurface cisterns. The labeling density ratio of clustered to scattered channels was about 60:1, established in SDS-FRL. Subsurface cisterns, also called hypolemmal cisterns, are subcompartments of the endoplasmic reticulum likely representing calciosomes that unload and refill Ca2+ independently. Purkinje cell subsurface cisterns are enriched in inositol 1,4,5-triphosphate receptors that mediate the effects of several neurotransmitters, hormones, and growth factors by releasing Ca2+ into the cytosol, generating local Ca2+ sparks. Such increases in cytosolic [Ca2+] may be sufficient for BK channel activation. Clustered BK channels in the plasma membrane may thus participate in building a functional unit (plasmerosome) with the underlying calciosome that contributes significantly to local signaling in Purkinje cells.
Kaufmann
Walter A
WA
Department of Pharmacology, Innsbruck Medical University, 6020 Innsbruck, Austria. walter.kaufmann@i-med.ac.at
Ferraguti
Francesco
F
Fukazawa
Yugo
Y
Kasugai
Yu
Y
Shigemoto
Ryuichi
R
Laake
Petter
P
Sexton
Joseph A
JA
Ruth
Peter
P
Wietzorrek
Georg
G
Knaus
Hans-Günther
HG
Storm
Johan F
JF
Ottersen
Ole Petter
OP
D000818:Animals; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D003713:Dendritic Cells / Q000378:metabolism; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005614:Freeze Fracturing; D007150:Immunohistochemistry; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000096:biosynthesis / Q000235:genetics; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011689:Purkinje Cells / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000096:biosynthesis / Q000235:genetics; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000235:genetics; D012967:Sodium Dodecyl Sulfate; D016610:Tissue Embedding; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D053496:Inositol 1,4,5-Trisphosphate Receptors; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D018091:Receptors, AMPA; D011963:Receptors, GABA-A; D012967:Sodium Dodecyl Sulfate; D005680:gamma-Aminobutyric Acid; C546241:Gabra1 protein, mouse; C465449:Kcnma1 protein, mouse