title: Evidence for the calcium-dependent potentiation of M-current obtained by the ratiometric measurement of the fura-2 fluorescence in bullfrog sympathetic neurons.
abstract: Intracellular Ca2+ concentration ([Ca]i) was measured following the activation of an inward Ca2+ current and subsequent potentiation of an M-type K+ current (IM) in bullfrog sympathetic neurons. Fura-2 was used as an indicator for [Ca]i. The fluorescence ratio at 340 and 380 nm (F340/F380) was elevated from 0.36 to 1.22 when IM was potentiated by 68% following the Ca2+ current. Based on the in vivo calibration curve obtained from cells permeabilized with digitonin (20 microM), the F340/F380 value of 1.22 was equivalent to a [Ca]i of 0.97 microM. We therefore propose that a rise in [Ca]i into the micromolar range can lead to the potentiation of IM in amphibian autonomic neurons.
authors.affiliation: Department of Physiology, Tokai University School of Medicine, Isehara, Japan. tokimasa@is.icc.u-tokai.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Tokimasa
authors.forename: T
authors.initials: T
authors.lastname: Shirasaki
authors.forename: K
authors.initials: K
authors.lastname: Kuba
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D016257:Fura-2; D009474:Neurons / Q000737:chemistry / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011892:Rana catesbeiana; D013564:Sympathetic Nervous System / Q000166:cytology*
chemical_list: D015221:Potassium Channels; D002118:Calcium; D016257:Fura-2