INVESTIGADORES
BARRANTES Francisco Jose
artículos
Título:
Effect of chemical modification of extracellular histidyl residues on the channel properties of the nicotinic acetylcholine receptor
Autor/es:
BOUZAT CB; LACORAZZA HD; JIMENEZ BONINO MB; BARRANTES FJ
Revista:
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY
Editorial:
SPRINGER
Referencias:
Lugar: Berlin; Año: 1993 vol. 423 p. 365 - 371
ISSN:
0031-6768
Resumen:
We have examined the effect of chemical modification with diethyl
pyrocarbonate (DEP) on the properties of acetylcholine(ACh)-activated
channels in the cloned muscle-cell line BC3H-1. After protein
modification, patch-clamp recordings showed alterations in the kinetics
of the nicotinic acetylcholine receptor (AChR) channel. The major effect
was observed in the channel mean open time, which was reduced up to
about 12-fold at 466 ìM DEP. The specificity of the effect was first
established through comparison with both untreated cells and cells
treated with inactivated DEP. Consistent with an increase in the number
of unprotonated histidine residues (pK
a=6.0),
this effect increased concomitantly with the pH of the reaction medium,
being faster at pH 8 than at pH 6. The changes were dependent on time
and DEP concentration, with an apparent EC50=114
ìM. Modified channels also showed an increase in the number of events
per burst of openings together with a decrease in burst durations. The
amplitude of the channelclosed time component of about 1 ms increased
with respect to the longest-duration-closed component. The number of á-bungarotoxin
sites was slightly reduced after the modification, without affecting
ligand binding affinity. The results suggest that DER affects
extracellular histidine residues involved in the ion translocation
function of the AChR, but not its toxin-recognition ability. DEP could,
therefore, induce a dissociation between toxin and agonist binding, as
is often observed in neuronal AChR.