M. Cohenarmon et M. Sokolovsky, EVIDENCE FOR INVOLVEMENT OF THE VOLTAGE-DEPENDENT NA-INDUCED ACTIVATION OF G-PROTEINS( CHANNEL GATING IN DEPOLARIZATION), The Journal of biological chemistry, 268(13), 1993, pp. 9824-9838
Evidence for activation of pertussis-toxin-sensitive G-proteins by mem
brane depolarization in rat brain-stem synaptoneurosomes was recently
reported (Coben-Armon, M., and Sokolovsky, M. (1991) J. Biol. Chem. 26
6, 2595-2605; (1991) Neurosci. Lett. 126, 87-90) and is further suppor
ted in this study by the observation that the depolarization-induced e
ffect is inhibited when G-proteins are stabilized in the non-activated
state with guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS), which was i
ntroduced into synaptoneurosomes during the process of permeabilizatio
n and resealing. In the present study, agents that either keep the vol
tage-dependent Na+ channel in persistently activated state (while Nacurrents are blocked) or prevent it from activation were used in an at
tempt to determine whether the voltage-dependent Na+ channels are invo
lved in the depolarization-induced activation of pertussis-toxin-sensi
tive G-proteins. The main probe employed was the cardiotonic and antia
rrhythmic agent DPI, which is a racemic mixture of two enantiomers, on
e of which (the R enantiomer) reportedly prevents depolarization-induc
ed activation of the Na+ channel while the other (the S enantiomer) in
hibits Na+ channel inactivation. The results suggest that while inacti
vation of the voltage-dependent Na+ channel does not interfere with th
e putative depolarization-induced activation of G-proteins, membrane d
epolarization affects G-proteins and the coupled muscarinic receptors
only if the voltage-dependent Na+ channels are capable of being activa
ted. Thus, inhibition of the depolarization-induced activation of Nachannels was accompanied by inhibition of the depolarization-induced a
ctivation of pertussis-toxin-sensitive G-proteins and by modifications
of both the coupling of G-proteins to muscarinic receptors and the AD
P-ribosylation of G(o)-proteins. These effects could be counteracted b
y persistent activation of the voltage-dependent Na+ channels (while N
a+ current was blocked). Our observations may suggest that the voltage
-dependent Na+ channel gating is involved in the depolarization-induce
d activation of pertussis toxin-sensitive G-proteins and may provide e
vidence for a possible mechanism of membrane depolarization signal tra
nsduction in excitable cells.