Gc. Bertran et Ba. Kotsias, CHLORIDE CURRENT IN TOAD SKELETAL-MUSCLE AND ITS MODIFICATION BY THE HISTIDINE-MODIFYING REAGENT DIETHYLPYROCARBONATE, Naunyn-Schmiedeberg's archives of pharmacology, 353(6), 1996, pp. 685-688
Cl- currents were measured in short fibres in the toad lumbricalis mus
cle with a two-microelectrode voltage clamp. Membrane Cl- conductance
increased markedly when external pH was raised. At pH 7 or higher, the
Cl- current fell during a hyperpolarizing voltage pulse and the rate
of inactivation was directly proportional to the voltage change. The h
istidine-modifying reagent diethylpyrocarbonate (DEPC, 1 mM) which car
bethoxylates histidil residues in proteins, suppressed the inactivatio
n of Cl- currents at pH 7.5. On the other hand, no apparent changes in
the kinetics of the currents at pH 5 were seen. NO3- currents, which
are independent of the extracellular pH and time, were not affected by
DEPC. Our results support the notion that the inactivation of Cl- cur
rents at pH 7.5 represents a membrane permeability change and that DEP
C interferes with this process. Protonation of histidine groups associ
ated with Cl- channels may be the controlling reaction for the pH-depe
ndent Cl- response.