Modulation of the gating of CIC-1 by S-(-) 2-(4-chlorophenoxy) propionic acid.
1. Using whole-cell patch-clamping and Sf-9 cells expressing the rat skeletal muscle chloride channel, rCIC-1, the cellular mechanism responsible for the myotonic side effects of clofibrate derivatives was examined. 2. RS-(+/-) 2-(4-chlorophenoxy)propionic acid (RS-(+/-) CPP) and its S-(-) enantiomer produced pronounced effects on CIC-1 gating. Both compounds caused the channels to deactivate more rapidly at hyperpolarizing potentials, which showed as a decrease in the time constants of both the fast and slow deactivating components of the whole cell currents. Both compounds also produced a concentration-dependent shift in the voltage dependence of channel apparent open probability to more depolarizing potentials, with an EC50 of 0.79 and 0.21 mM for the racemate and S-(-) enantiomer respectively. R-(+) CPP at similar concentrations had no effect on gating. RS-(+/-) CPP did not block the passage of Cl- through the pore of rCIC-1. 3. CIC-1 is gated by Cl- binding to a site within an access channel and S-(-) CPP alters gating of the channel by decreasing the affinity of this binding site for Cl-. Comparison of the EC50 for RS-(+/-) CPP and S-(-) CPP indicates that R-(+) CPP can compete with the S-(-) enantiomer for the site but that it is without biological activity. 4. RS-(+/-) CPP produced the same effect on rCIC-1 gating when added to the interior of the cell and in the extracellular solution. 5. S-(-) CPP modulates the gating of CIC-1 to decrease the membrane Cl- conductance (GCl), which would account for the myotonic side effects of clofibrate and its derivatives.
Aromataris
E C
EC
Department of Physiology, University of Adelaide, South Australia, Australia.
Astill
D S
DS
Rychkov
G Y
GY
Bryant
S H
SH
Bretag
A H
AH
Roberts
M L
ML
D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D018118:Chloride Channels / Q000187:drug effects* / Q000502:physiology; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009124:Muscle Proteins / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D013237:Stereoisomerism
C086321:CLC-1 channel; D018118:Chloride Channels; D002712:Chlorides; D009124:Muscle Proteins; C048213:2-(4-chlorophenoxy)propionic acid; D008456:2-Methyl-4-chlorophenoxyacetic Acid