Modification of frequency augmentation-potentiation by GTP gamma S in the frog neuromuscular junction.
The effect of modifiers of guanine nucleotide-binding proteins (G proteins) on the frequency augmentation-potentiation of transmitter release were studied in the frog neuromuscular junction. Using Genetransfer as a carrier the mean quantal content of the endplate potential increased by penetration of GTP gamma S into the presynaptic nerve terminal. Neither GTP gamma S alone nor carrier alone had any effect. The relationship of log (mean quantal content) versus stimulation frequency changed from a single linear to a dual linear function, suggesting that the immediately releasable pool was modified. GDP beta S + carrier also had similar effects, but was less potent. Aluminium fluoride was without effect. Extracellularly recorded presynaptic nerve action potentials remained unchanged with GTP gamma S + carrier. Also, GTP gamma S + carrier did not affect the action potential nor the cytosolic Ca2+ concentration in differentiated NG108-15 hybrid cells. It is suggested that some smg-type G protein-dependent processes are involved in determining frequency augmentation-potentiation.
Enomoto
K
K
Department of Physiology, Shimane Medical University, Japan.
Maeno
T
T
D000200:Action Potentials; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000502:physiology; D011898:Ranidae; D013873:Thionucleotides / Q000494:pharmacology
D017607:Aluminum Compounds; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D019204:GTP-Binding Proteins; D005459:Fluorides; C032311:aluminum fluoride