Single Ca-activated cation channels in bursting neurons ofHelix |
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Authors: | L D Partridge D Swandulla |
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Institution: | (1) Department of Neurophysiology, Max-Planck-Institute for Psychiatry, D-8033 Martinsried;(2) Department of Physiology, University of New Mexico School of Medicine, 87131 Albuquerque, New Mexico, USA;(3) Present address: Max-Planck-Institute at the Department of Physiology, University of Pennsylvania, School of Medicine, 19104 Philadelphia, PA, USA |
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Abstract: | The depolarizing drive that maintains bursting inHelix neurons is carried by a long-lasting calcium-activated inward current. This current was studied using cell-attached and inside-out patches from the right parietal fast burster neuron ofHelix pomatia.One population of unitary currents was inward at –50 mV and showed an increased probability of opening when Ca2+ was injected or when excised patches were bathed in solutions with 10–7 to 10–5 M free Ca2+ levels. Cell-attached patches (patch electrodes filled with 10–7 M Ca2+ Ringer) had single channel conductances near 30 pS with reversal potentials near –20 mV; excised patches had similar conductances in symmetrical Na+ solutions and reversal potentials within a few millivolts of zero. Calculations, assuming a simple spherical cell, yield a channel density of only about 1/6 m2. The increased channel opening probability characteristically persisted well beyond the duration of transient whole-cell inward current. We conclude from this that the later phase of Ca-activated inward currents is normally masked by outward currents. |
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Keywords: | Helix bursting neurons Single channel recordings Ca-activated nonspecific currents |
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