[The gating mechanism of K(+)-channels coupled to the FMRFamide receptor in the ganglion cells of Aplysia].
1. Neurons with a receptor responded to FMRFamide (Phe-Met-Arg-Phe-NH2) were identified in the ganglion of Aplysia kurodai. Ionic mechanism and channel gating system of the FMRFamide-induced responses were investigated by current clamp and voltage clamp methods. 2. The reversal potential of FMRFamide-induced response exactly coincided with the equilibrium potential for K+. This proved that the response was produced by a specific increase in membrane permeability toward K+, exclusively. 3. The FMRFamide-induced response was not affected by the inhibitors for Ca2(+)-activated K(+)-current, i.e., TEA, apamin, and EGTA. This excluded a possibility that FMRFamide-activated K(+)-channel is a Ca2(+)-activated K(+)-channel. 4. Intracellular injection of pertussis-toxin (PTX) caused no change in either resting potential or conductance, but it irreversibly blocked the FMRFamide-induced outward current within 30 min. Similarly applied cholera toxin (CTX) showed no effect on the FMRF-amide response. 5. Intracellular application of guanosine 5'-0-(2-thiodiphosphate) (GDP beta S) caused no effect on either resting potential or conductance, but it blocked the FMRFamide-induced K(+)-current within 3 min. 6. Intracellular application of guanosine 5'-0-(3-thiotriphosphate) (GTP gamma S) alone induced a slowly developing, irreversible outward current associated with an increase in membrane conductance. However, repetitive applications of FMRFamide immediately after the start of GTP gamma S application markedly facilitated the effect of GTP gamma S on the resting membrane. 7. Intracellular application of either adenylate cyclase inhibitor (3'-deoxyadenosine) or A-kinase inhibitor (H-8) did not affect the FMRFamide-induced response. 8. It was concluded that the FMRFamide-induced K(+)-current is mediated by PTX-sensitive GTP-binding protein Gi, Go or Gk. It was also suggested that the FMRFamide-induced response is produced independently of the changes in intracellular Ca2+ or cyclic AMP.
Takahashi
J
J
Department of Physiology, School of medicine, Iwata Medical University, Japan.
Sasaki
K
K
Matsumoto
M
M
D037361:Adenylate Cyclase Toxin; D000818:Animals; D001048:Aplysia; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability; D004553:Electric Conductivity / Q000187:drug effects; D005724:Ganglia / Q000166:cytology / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000031:analogs & derivatives; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D037342:Pertussis Toxin; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000502:physiology*; D018010:Receptors, Invertebrate Peptide; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; C055209:FMRFamide receptor; D015221:Potassium Channels; D011956:Receptors, Cell Surface; D018010:Receptors, Invertebrate Peptide; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; C034883:guanosine 5'-O-(2-thiotriphosphate); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D011188:Potassium; D002118:Calcium