The Ca2+-dependent slow K+ conductance in cultured rat muscle cells: characterization with apamin.
The interaction of apamin, a bee venom neurotoxin, with rat skeletal muscle cell membranes has been followed using both an electrophysiological and a biochemical approach. Voltage-clamp analyses have shown that apamin, at low concentrations, specifically blocks the Ca2+-dependent slow K+ conductance in rat myotubes and myosacs . A specific binding site for apamin in rat muscle cell membranes has been characterized with the use of a highly radiolabelled apamin derivative [( 125I]apamin). The dissociation constant for the apamin-receptor complex is 36-60 pM and the maximal binding capacity is 3.5 fmol/mg of protein. [125I]Apamin binding to rat muscle membranes is displaced by quinine and quinidine with K0.5 values of 110 microM and 200 microM, respectively.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000831:Animals, Newborn; D001030:Apamin / Q000378:metabolism / Q000633:toxicity*; D001514:Bee Venoms / Q000633:toxicity*; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004553:Electric Conductivity / Q000187:drug effects; D005071:Evoked Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism
D001514:Bee Venoms; D015221:Potassium Channels; D011956:Receptors, Cell Surface; C033799:apamin receptor; D001030:Apamin; D011188:Potassium; D002118:Calcium