G-protein mediating the slow depolarization induced by FMRFamide in the ganglion cells of Aplysia.
Application of FMRFamide (Phe-Met-Arg-Phe-NH2) induced a slow depolarization in neurons of the Aplysia abdominal ganglion. In voltage-clamped cells, FMRFamide induced a slow inward current that increased when the membrane was depolarized beyond -85 mV, showing a negative slope conductance. However, this inward current never reversed to outward current when hyperpolarized beyond the equilibrium potential for K+. The FMRFamide-induced response was markedly augmented in Ca(2+)-free media, but depressed in Na(+)-free media. It was unaffected by a change in external potassium. Intracellular injection of guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) significantly depressed the FMRFamide response in a dose-dependent way. Injection of cholera toxin (CTX) which did not cause any current response, selectively and irreversibly blocked the FMRFamide response. Neither 3'-deoxyadenosine, an inhibitor of adenylate cyclase, nor H-8, an inhibitor of cyclic adenosine 3',5'-monophosphate (cyclic AMP)-dependent kinase, depressed the FMRFamide response. 3-Isobutyl-1-methylxanthine (IBMX) did not augment the FMRFamide response appreciably. The FMRFamide response was not occluded at all by a relatively large injection of 8-bromo-cyclic AMP. It was concluded that the FMRFamide response is produced by the opening of the voltage-dependent Na(+)-channels via activation of a certain CTX-sensitive G-protein which is different from conventional "Gs" that activates adenylate cyclase.
Chiba
O
O
Department of Physiology, School of Medicine, Iwate Medical University, Japan.
Sasaki
K
K
Higuchi
H
H
Takashima
K
K
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000595:Amino Acid Sequence; D000818:Animals; D001048:Aplysia / Q000502:physiology*; D002772:Cholera Toxin / Q000494:pharmacology; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D019835:FMRFamide; D019204:GTP-Binding Proteins / Q000502:physiology*; D005724:Ganglia / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010477:Perfusion; D047428:Protein Kinase Inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D007473:Ion Channels; D009467:Neuromuscular Depolarizing Agents; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D047428:Protein Kinase Inhibitors; D010566:Virulence Factors, Bordetella; D015124:8-Bromo Cyclic Adenosine Monophosphate; D005680:gamma-Aminobutyric Acid; D019835:FMRFamide; D002772:Cholera Toxin; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D015056:1-Methyl-3-isobutylxanthine