RT Journal Article
SR Electronic
T1 Evidence for a Common Pharmacological Interaction Site on K<sub>Ca</sub>2 Channels Providing Both Selective Activation and Selective Inhibition of the Human K<sub>Ca</sub>2.1 Subtype
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 210
OP 219
DO 10.1124/mol.111.074252
VO 81
IS 2
A1 Charlotte Hougaard
A1 Sofia Hammami
A1 Birgitte L. Eriksen
A1 Ulrik S. Sørensen
A1 Marianne L. Jensen
A1 Dorte Strøbæk
A1 Palle Christophersen
YR 2012
UL http://molpharm.aspetjournals.org/content/81/2/210.abstract
AB We have previously identified Ser293 in transmembrane segment 5 as a determinant for selective KCa2.1 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 KCa2.1: 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 KCa2.1 channel. Whereas (−)-CM-TPMF activates KCa2.1 with an EC50 value of 24 nM, (−)-B-TPMF inhibits the channel with an IC50 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 KCa2 channels and the KCa3 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 KCa2.1 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 KCa2.1 than NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime), an unselective but hitherto the most potent KCa3/KCa2 channel activator. (−)-B-TPMF is the first small-molecule inhibitor with significant selectivity among the KCa2 channel subtypes. In contrast to peptide blockers such as apamin and scyllatoxin, which preferentially affect KCa2.2, (−)-B-TPMF exhibits KCa2.1 selectivity. These high-affinity compounds, which exert opposite effects on KCa2.1 gating, may help define physiological or pathophysiological roles of this channel.