Ki. Enomoto et T. Maeno, MODIFICATION OF FREQUENCY AUGMENTATION-POTENTIATION BY GTP-GAMMA-S INTHE FROG NEUROMUSCULAR-JUNCTION, Cell biochemistry and function, 13(2), 1995, pp. 105-109
The effect of modifiers of guanine nucleotide-binding proteins (G prot
eins) on the frequency augmentation-potentiation of transmitter releas
e were studied in the frog neuromuscular junction. Using Genetransfer(
R) as a carrier the mean quantal content of the endplate potential inc
reased by penetration of GTP gamma S into the presynaptic nerve termin
al. Neither GTP gamma S alone nor carrier alone had any effect. The re
lationship of log (mean quantal content) versus stimulation frequency
changed from a single linear to a dual linear function, suggesting tha
t the immediately releasable pool was modified. GDP beta S + carrier a
lso had similar effects, but was less potent. Aluminium fluoride was w
ithout effect. Extracellularly recorded presynaptic nerve action poten
tials remained unchanged with GTP gamma S + carrier. Also, GTP gamma S
+ carrier did not affect the action potential nor the cytosolic Ca2concentration in differentiated NG108-15 hybrid cells. It is suggested
that some smg-type G protein-dependent processes are involved in dete
rmining frequency augmentation-potentiation.