Benzocaine enhances and inhibits the K+ current through a human cardiac cloned channel (Kv1.5).
OBJECTIVE
The aim of this study was to analyze the effects of a neutral local anaesthetic, benzocaine, on a cardiac K+ channel cloned from human ventricle.


METHODS
Experiments were performed on hKv1.5 channels stably expressed on mouse cells using the whole-cell configuration of the patch clamp technique.


RESULTS
At 10 nM, benzocaine increased the current amplitude ("agonist effect") by shifting the activation curve 8.4 +/- 2.7 mV in the negative direction, and slowed the time course of tail current decline. In contrast, benzocaine (100-700 microM) inhibited hKv1.5 currents (KD = 901 +/- 81 microM), modified the voltage-dependence of channel activation, which became biphasic, and accelerated the channel deactivation. Extracellular K+ concentration ([K+]o) also affected the channel gating. At 140 mM [K+]o, the time course of tail currents deactivation was significantly accelerated, whereas at 0 mM [K+]o, it was slowed. At both [K+]o the activation curve became biphasic. Benzocaine accelerated the tail current decay at 0 mM but not at 140 mM [K+]o. The reduction in the permeation of K+ through the pore did not modify the blocking effects of micromolar concentrations of benzocaine, but suppressed the agonist effect observed at nanomolar concentrations.


CONCLUSIONS
All these results suggest that benzocaine blocks and modifies the voltage- and time-dependent properties of hKv1.5 channels, binding to an extracellular and to an intracellular site at the channel level. Moreover, both sites are related to each other and can also interact with K+.
Delpón
E
E
Department of Pharmacology, School of Medicine, Universidad Complutense, Madrid, Spain. edelpon@eucmax.sim.ucm.es
Caballero
R
R
Valenzuela
C
C
Longobardo
M
M
Snyders
D
D
Tamargo
J
J
D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology*; D001566:Benzocaine / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects*; D003001:Cloning, Molecular; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D017136:Ion Transport; D051666:Kv1.5 Potassium Channel; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D011485:Protein Binding; D013997:Time Factors
D000779:Anesthetics, Local; C496981:KCNA5 protein, human; D051666:Kv1.5 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011188:Potassium; D001566:Benzocaine