|
|
|
|
|
|
|
||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Evidence for Drug Binding Along the Activation Pathway
2 Department of Biology, Clarkson University, Potsdam, NY 13699
3 Department of Anesthesia, Harvard Medical School and Brigham and Women's Hospital, Boston, MA 02115
Address correspondence to Ging Kuo Wang, Dept. of Anesthesia, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115. Fax: 617730-2801; email:wang{at}zeus.bwh.harvard.edu
According to the classic modulated receptor hypothesis, local anesthetics (LAs) such as benzocaine and lidocaine bind preferentially to fast-inactivated Na+ channels with higher affinities. However, an alternative view suggests that activation of Na+ channels plays a crucial role in promoting high-affinity LA binding and that fast inactivation per se is not a prerequisite for LA preferential binding. We investigated the role of activation in LA action in inactivation-deficient rat muscle Na+ channels (rNav1.4-L435W/L437C/A438W) expressed in stably transfected Hek293 cells. The 50% inhibitory concentrations (IC50) for the open-channel block at +30 mV by lidocaine and benzocaine were 20.9 ± 3.3 µM (n = 5) and 81.7 ± 10.6 µM (n = 5), respectively; both were comparable to inactivated-channel affinities. In comparison, IC50 values for resting-channel block at –140 mV were >12-fold higher than those for open-channel block. With 300 µM benzocaine, rapid time-dependent block (
0.8 ms) of inactivation-deficient Na+ currents occurred at +30 mV, but such a rapid time-dependent block was not evident at –30 mV. The peak current at –30 mV, however, was reduced more severely than that at +30 mV. This phenomenon suggested that the LA block of intermediate closed states took place notably when channel activation was slow. Such closed-channel block also readily accounted for the LA-induced hyperpolarizing shift in the conventional steady-state inactivation measurement. Our data together illustrate that the Na+ channel activation pathway, including most, if not all, transient intermediate closed states and the final open state, promotes high-affinity LA binding.
Key Words: sodium channel • fast inactivation • persistent sodium currents • local anesthetics • modulated receptor hypothesis
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  G. K. Wang, J. Calderon, and S.-Y. Wang State- and Use-Dependent Block of Muscle Nav1.4 and Neuronal Nav1.7 Voltage-Gated Na+ Channel Isoforms by Ranolazine Mol. Pharmacol., March 1, 2008; 73(3): 940 - 948. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W. Ouyang, T.-Y. Jih, T.-T. Zhang, A. M. Correa, and H. C. Hemmings Jr. Isoflurane Inhibits NaChBac, a Prokaryotic Voltage-Gated Sodium Channel J. Pharmacol. Exp. Ther., September 1, 2007; 322(3): 1076 - 1083. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. P. Beekwilder, G. Th.H. van Kempen, R. J. van den Berg, and D. L. Ypey The Local Anesthetic Butamben Inhibits and Accelerates Low-Voltage Activated T-Type Currents in Small Sensory Neurons Anesth. Analg., January 1, 2006; 102(1): 141 - 145. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. M. Lipkind and H. A. Fozzard Molecular Modeling of Local Anesthetic Drug Binding by Voltage-Gated Sodium Channels Mol. Pharmacol., December 1, 2005; 68(6): 1611 - 1622. [Abstract] [Full Text] [PDF]
|
|
|
|
