title: Biophysical properties of voltage-gated Na+ channels in frog parathyroid cells and their modulation by cannabinoids.
abstract: The membrane properties of isolated frog parathyroid cells were studied using perforated and conventional whole-cell patch-clamp techniques. Frog parathyroid cells displayed transient inward currents in response to depolarizing pulses from a holding potential of -84 mV. We analyzed the biophysical properties of the inward currents. The inward currents disappeared by the replacement of external Na+ with NMDG+ and were reversibly inhibited by 3 micromol l-1 TTX, indicating that the currents occur through the TTX-sensitive voltage-gated Na+ channels. Current density elicited by a voltage step from -84 mV to -24 mV was -80 pA pF-1 in perforated mode and -55 pA pF-1 in conventional mode. Current density was decreased to -12 pA pF-1 by internal GTPgammaS (0.5 mmol l-1), but not affected by internal GDPbetaS (1 mmol l-1). The voltage of half-maximum (V1/2) activation was -46 mV in both perforated and conventional modes. V1/2 of inactivation was -80 mV in perforated mode and -86 mV in conventional mode. Internal GTPgammaS (0.5 mmol l-1) shifted the V1/2 for activation to -36 mV and for inactivation to -98 mV. A putative endocannabinoid, 2-arachidonoylglycerol ether (2-AG ether, 50 micromol l-1) and a cannabinomimetic aminoalkylindole, WIN 55,212-2 (10 micromol l-1) also greatly reduced the Na+ current and shifted the V1/2 for activation and inactivation. The results suggest that the Na+ currents in frog parathyroid cells can be modulated by cannabinoids via a G protein-dependent mechanism.
authors.affiliation: Integrative Sensory Physiology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Nagasaki 852-8588, Japan. okada@net.nagasaki-u.ac.jp
authors.forename: Yukio
authors.initials: Y
authors.lastname: Okada
authors.forename: Kotapola G
authors.initials: KG
authors.lastname: Imendra
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Miyazaki
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hotokezaka
authors.forename: Rie
authors.initials: R
authors.lastname: Fujiyama
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Zeredo
authors.forename: Takenori
authors.initials: T
authors.lastname: Miyamoto
authors.forename: Kazuo
authors.initials: K
authors.lastname: Toda
mesh_terms: D000818:Animals; D001703:Biophysics / Q000379:methods; D002186:Cannabinoids / Q000494:pharmacology*; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D010280:Parathyroid Glands / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011892:Rana catesbeiana / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D002186:Cannabinoids; D015222:Sodium Channels; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D019204:GTP-Binding Proteins