Kvbeta1.3 reduces the degree of stereoselective bupivacaine block of Kv1.5 channels.
BACKGROUND
Kvbeta1.3 subunit modifies the gating and the pharmacology of Kv1.5 channels, decreasing their sensitivity to block induced by drugs, suggesting that Kvbeta1.3 competes with them for a binding site at Kv1.5 channels.


METHODS
Currents generated by the activation of Kv1.5 and Kv1.5 + Kvbeta1.3 channels expressed in HEK293 cells and Xenopus oocytes were recorded by using whole cell patch clamp and voltage clamp techniques.


RESULTS
Block of Kv1.5, but not that produced on Kv1.5 + Kvbeta1.3 channels, was voltage dependent. In both channels, bupivacaine block was time dependent. R(+)- and S(-)-bupivacaine blocked Kv1.5 with IC50 4.4 +/- 0.5 microM (n = 15) and 39.8 +/- 8.2 microM (n = 16; P < 0.05), respectively. These values increased fourfold for R(+)-bupivacaine (17.2 +/- 2.2 microM) and twofold for S(-)-bupivacaine (71.9 +/- 11.5 microM) in Kv1.5 + Kvbeta1.3 channels. Therefore, the degree of stereoselectivity (theta) decreased from 9 to 4 in the presence of Kvbeta1.3. The decrease in potency to block Kv1.5 + Kvbeta1.3 channels was the result of a less stable interaction between bupivacaine enantiomers and channels. Differences in stereoselectivity in each situation were due to a more favorable interaction between the channel and R(+)-bupivacaine. In the presence of Kvbeta1.3, stereoselectivity was abolished for V514A mutant channels (involved in bupivacaine binding but not in Kvbeta1.3 binding) but not for L510A (part of Kvbeta1.3 binding site).


CONCLUSIONS
The degree of stereoselective block of Kv1.5 decreases from 9 to 4 when Kvbeta1.3 is present. L510 is determinant for the modulation of bupivacaine block, because it is the only residue of the S6 segment that binds to both bupivacaine and Kvbeta1.3. These findings support an overlapping binding site for drugs and Kvbeta1.3.
Arias
Cristina
C
Institute of Pharmacology and Toxicology, Consejo Superior de Investigaciones Científicas/Universidad Complutense de Madrid, School of Medicine, Universidad Complutense, Madrid, Spain.
Guizy
Miriam
M
David
Miren
M
Marzian
Stefanie
S
González
Teresa
T
Decher
Niels
N
Valenzuela
Carmen
C
D000465:Algorithms; D000779:Anesthetics, Local / Q000737:chemistry* / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D002045:Bupivacaine / Q000737:chemistry* / Q000494:pharmacology*; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D051664:Kv1.3 Potassium Channel / Q000235:genetics / Q000502:physiology*; D051666:Kv1.5 Potassium Channel / Q000187:drug effects* / Q000235:genetics; D009154:Mutation / Q000235:genetics / Q000502:physiology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D013237:Stereoisomerism; D014162:Transfection; D014982:Xenopus laevis
D000779:Anesthetics, Local; C097044:KCNAB1 protein, human; D051664:Kv1.3 Potassium Channel; D051666:Kv1.5 Potassium Channel; D026902:Potassium Channel Blockers; D002045:Bupivacaine