title: Activation of beta-adrenergic receptor induces Na(+)-dependent inward currents in acutely dissociated motoneurons of bullfrog spinal cord.
abstract: Effects of adrenergic drugs on single motoneurons acutely dissociated from the lumbar enlargement of adult bullfrogs were examined. The dissociated large cells were identified as motoneurons by retrograde labeling with a fluorescent dye. Adrenaline caused membrane depolarization with a decrease in input resistance. Under whole-cell voltage clamp conditions at a holding potential of -70 mV, adrenergic drugs induced inward currents in a dose-dependent manner. Adrenaline was more potent than noradrenaline. Under K(+)-free conditions, adrenaline (10(-6)-10(-5) M) induced inward currents which were blocked by propranolol (10(-6) M) but not by phentolamine (10(-5) M). CoCl2 (1 mM) did not affect the currents. Substitution of choline+ in the recording solution for Na+ abolished the currents, but tetrodotoxin (TTX, 10(-6) M) had no effect on them. The adrenaline-induced currents exhibited a characteristic voltage-dependency: the conductance became large at hyperpolarized membrane potential (-150 to -30 mV) and approached zero at the depolarized membrane potential (greater than -30 mV), but was never reversed up to 30 mV, suggesting that the currents are different from non-specific cation currents. Substitution of isethionate- for Cl- in the recording solution had no effect on the voltage-dependency of the adrenaline-induced currents, whereas substitution of choline+ for Na+ apparently attenuated the voltage-dependency of the currents. These results indicate that adrenaline induces Na(+)-dependent inward currents through activation of beta-adrenergic receptors in bullfrog motoneurons.
authors.affiliation: Department of Toxicology and Pharmacology, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Adachi
authors.forename: J
authors.initials: J
authors.lastname: Oka
authors.forename: T
authors.initials: T
authors.lastname: Nagao
authors.forename: H
authors.initials: H
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D002794:Choline / Q000494:pharmacology; D004553:Electric Conductivity; D004837:Epinephrine / Q000494:pharmacology; D007477:Ions; D008564:Membrane Potentials; D009046:Motor Neurons / Q000502:physiology*; D011892:Rana catesbeiana; D011943:Receptors, Adrenergic, beta / Q000737:chemistry / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*
chemical_list: D007477:Ions; D011943:Receptors, Adrenergic, beta; D012964:Sodium; D002794:Choline; D004837:Epinephrine