TY - JOUR
T1 - Pharmacology of the high-affinity apamin receptor in rabbit heart
AU - Schetz, John A.
AU - Anderson, Peter A.V.
PY - 1995/11
Y1 - 1995/11
N2 - Apamin is a potent blocker of calcium-activated small conductance potassium (SK) channels in neurons, liver, skeletal muscle and ileum smooth muscle, but not in cardiac muscle. Cardiac muscle is devoid of SK channels; however, in isolated, single ventricular myocytes apamin is an extremely potent blocker of the L-type calcium current, and the anti-arrhythmic drug quinidine reverses apamin block. Objective: To characterize the receptor binding properties and pharmacology of the apamin receptor in heart. Methods: The binding properties of the apamin receptor were determined by rapid filtration of purified rabbit heart membranes. Results: Monoiodinated apamin binds to a labile, membrane-bound protein in heart membranes at a single, high-affinity site (KD = 8.07 ± 2.14 pM and Bmax = 686 ± 167 fmoles/mg protein, significant run test at P = 0.05 for a one site fit).125I-apamin binding is dose-dependently inhibited by apamin, scyllatoxin, quinidine, amiloride, as well as a variety of di- and trivalent cations that are classical blockers of L-type calcium channels (e.g. Co2+, Cd2+, Mn2+, La3+, Gd3+). The cardiac apamin receptor is also critically dependent upon pH, temperature and KCl, and co-purifies in the same membrane fraction as L-type cardiac Ca2+ channels. Conclusions: The apamin receptor in rabbit heart P2 membranes has pharmacological and biochemical properties in common with both an SK channel and an L-type Ca2+ channel.
AB - Apamin is a potent blocker of calcium-activated small conductance potassium (SK) channels in neurons, liver, skeletal muscle and ileum smooth muscle, but not in cardiac muscle. Cardiac muscle is devoid of SK channels; however, in isolated, single ventricular myocytes apamin is an extremely potent blocker of the L-type calcium current, and the anti-arrhythmic drug quinidine reverses apamin block. Objective: To characterize the receptor binding properties and pharmacology of the apamin receptor in heart. Methods: The binding properties of the apamin receptor were determined by rapid filtration of purified rabbit heart membranes. Results: Monoiodinated apamin binds to a labile, membrane-bound protein in heart membranes at a single, high-affinity site (KD = 8.07 ± 2.14 pM and Bmax = 686 ± 167 fmoles/mg protein, significant run test at P = 0.05 for a one site fit).125I-apamin binding is dose-dependently inhibited by apamin, scyllatoxin, quinidine, amiloride, as well as a variety of di- and trivalent cations that are classical blockers of L-type calcium channels (e.g. Co2+, Cd2+, Mn2+, La3+, Gd3+). The cardiac apamin receptor is also critically dependent upon pH, temperature and KCl, and co-purifies in the same membrane fraction as L-type cardiac Ca2+ channels. Conclusions: The apamin receptor in rabbit heart P2 membranes has pharmacological and biochemical properties in common with both an SK channel and an L-type Ca2+ channel.
KW - Apamin
KW - Apamin receptor
KW - Calcium channels
KW - Potassium channel
KW - Quinidine
KW - Rabbit, ventricular myocytes
KW - SK
UR - http://www.scopus.com/inward/record.url?scp=0028806276&partnerID=8YFLogxK
U2 - 10.1016/S0008-6363(95)00114-X
DO - 10.1016/S0008-6363(95)00114-X
M3 - Article
C2 - 8595623
AN - SCOPUS:0028806276
SN - 0008-6363
VL - 30
SP - 755
EP - 762
JO - Cardiovascular Research
JF - Cardiovascular Research
IS - 5
ER -