title: Evidence for a common pharmacological interaction site on K(Ca)2 channels providing both selective activation and selective inhibition of the human K(Ca)2.1 subtype.
abstract: We have previously identified Ser293 in transmembrane segment 5 as a determinant for selective K(Ca)2.1 channel activation by GW542573X (4-(2-methoxyphenylcarbamoyloxymethyl)-piperidine-1-carboxylic acid tert-butyl ester). Now we show that Ser293 mediates both activation and inhibition of K(Ca)2.1: CM-TPMF (N-{7-[1-(4-chloro-2-methylphenoxy)ethyl]-[1,2,4]triazolo[1,5-a]pyrimidin-2-yl}-N'-methoxy-formamidine) and B-TPMF (N-{7-[1-(4-tert-butyl-phenoxy)ethyl]-[1,2,4]triazolo[1,5-a]pyrimidin-2-yl}-N'-methoxy-formamidine), two newly identified and structurally related [1,2,4]triazolo[1,5-a]pyrimidines, act either as activators or as inhibitors of the human K(Ca)2.1 channel. Whereas (-)-CM-TPMF activates K(Ca)2.1 with an EC(50) value of 24 nM, (-)-B-TPMF inhibits the channel with an IC(50) value of 31 nM. In contrast, their (+)-enantiomers are 40 to 100 times less active. Both (-)-CM-TPMF and (-)-B-TPMF are subtype-selective, with 10- to 20-fold discrimination toward other K(Ca)2 channels and the K(Ca)3 channel. Coapplication experiments reveal competitive-like functional interactions between the effects of (-)-CM-TPMF and (-)-B-TPMF. Despite belonging to a different chemical class than GW542573X, the K(Ca)2.1 selectivity of (-)-CM-TPMF and (-)-B-TPMF depend critically on Ser293 as revealed by loss- and gain-of-function mutations. We conclude that compounds occupying the TPMF site may either positively or negatively influence the gating process depending on their substitution patterns. It is noteworthy that (-)-CM-TPMF is 10 times more potent on K(Ca)2.1 than NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime), an unselective but hitherto the most potent K(Ca)3/K(Ca)2 channel activator. (-)-B-TPMF is the first small-molecule inhibitor with significant selectivity among the K(Ca)2 channel subtypes. In contrast to peptide blockers such as apamin and scyllatoxin, which preferentially affect K(Ca)2.2, (-)-B-TPMF exhibits K(Ca)2.1 selectivity. These high-affinity compounds, which exert opposite effects on K(Ca)2.1 gating, may help define physiological or pathophysiological roles of this channel.
authors: NeuroSearch A/S, Ballerup, Denmark.
authors: Charlotte
authors: C
authors: Hougaard
authors: Sofia
authors: S
authors: Hammami
authors: Birgitte L
authors: BL
authors: Eriksen
authors: Ulrik S
authors: US
authors: Sørensen
authors: Marianne L
authors: ML
authors: Jensen
authors: Dorte
authors: D
authors: Strøbæk
authors: Palle
authors: P
authors: Christophersen
mesh_terms: D019943:Amino Acid Substitution; D001665:Binding Sites; D006801:Humans; D020128:Inhibitory Concentration 50; D015640:Ion Channel Gating / Q000187:drug effects; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000819:agonists / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000235:genetics; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D051640:Small-Conductance Calcium-Activated Potassium Channels