title: Separation of ionic currents in the somatic membrane of frog sensory neurons.
abstract: Electrical properties of isolated frog primary afferent neurons were examined by suction pipette technique, which combines internal perfusion with current or voltage clamp using a switching circuit with a single electrode. When K+ in the external and internal solutions was totally replaced with Cs+, extremely prolonged Ca spikes, lasting for 5 to 10 sec, and Na spikes, having a short plateau phase of 10 to 15 msec, were observed in Na+-free and Ca2+-free solutions, respectively. Under voltage clamp, Ca2+ current (ICa) appeared at around -30 mV and maximum peak current was elicited at about 0 mV. With increasing test pulses to the positive side, ICa became smaller and flattened but did not reverse. Increases of [Ca]o induced a hyperbolic increase of ICa and also shifted its I-V curve along the voltage axis to the more positive direction. Internal perfusion of F- blocked ICa time-dependently. The Ca channel was permeable to foreign divalent cations in the sequence of ICa greater than IBa greater than ISr much greater than IMn greater than IZn. Organic Ca-blockers equally depressed the divalent cation currents dose- and time-dependently without shifting the I-V relationships, while inorganic blockers suppressed these currents dose-dependently and the inhibition appeared much stronger in the order of IBa = ISr greater than ICa greater than IMn = IZn.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology; D003217:Conductometry / Q000295:instrumentation; D005727:Ganglia, Spinal / Q000166:cytology; D007473:Ion Channels / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011892:Rana catesbeiana / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D002412:Cations; D007473:Ion Channels; D011188:Potassium; D002118:Calcium