Comparable 30-kDa apamin binding polypeptides may fulfill equivalent roles within putative subtypes of small conductance Ca(2+)-activated K+ channels.
Apamin, a peptide neurotoxin from bee venom, blocks small conductance Ca(2+)-activated K+ channels in central synapses and peripheral tissues. Using 125I-apamin, single classes of high affinity binding sites (Kd 1-3 pM) were identified on plasma membranes from rat, rabbit, guinea pig, and bovine brain and from rabbit, guinea pig, and bovine liver. Binding was sensitive to scyllatoxin, dequalinium, gallamine, and d-tubocurarine but not to charybdotoxin, toxin I, or mast cell degranulating peptide. In contrast, saturable binding of 125I-apamin to rat liver plasma membranes was virtually undetectable, thereby providing a correlation with the ability to measure apamin-sensitive Ca(2+)-activated potassium currents in rabbit and guinea pig hepatocytes but not in rat hepatocytes. In agreement with membrane binding studies, homobifunctional cross-linkers identified apparently identical 33-kDa 125I-apamin binding polypeptides on brain plasma membranes from all species and analogous but distinct polypeptides on plasma membranes from rabbit, guinea pig, and bovine liver. None of these affinity-labeled polypeptides were detectable on plasma membranes from rat liver. Affinity labeling was abolished on both liver and brain membranes by apamin, scyllatoxin, dequalinium, gallamine, and d-tubocurarine. These results indicate that comparable approximately 30-kDa polypeptides may fulfill equivalent functional roles within putative subtypes of apamin-sensitive small conductance Ca(2+)-activated K+ channels.
Department of Paediatrics and Neonatal Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
J D
JD
Wadsworth
K B
KB
Doorty
P N
PN
Strong
D000818:Animals; D001030:Apamin / Q000378:metabolism*; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D006168:Guinea Pigs; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure; D008564:Membrane Potentials; D009466:Neuromuscular Blocking Agents / Q000494:pharmacology; D009498:Neurotoxins / Q000494:pharmacology; D010455:Peptides / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D011817:Rabbits; D051381:Rats
D009466:Neuromuscular Blocking Agents; D009498:Neurotoxins; D010455:Peptides; D015221:Potassium Channels; C033799:apamin receptor; D001030:Apamin; D002118:Calcium