Pflügers Archiv

, Volume 410, Issue 3, pp 234–242 | Cite as

The Ca2+-sensitive K+-currents underlying the slow afterhyperpolarization of bullfrog sympathetic neurones

  • Kohichi Tanaka
  • Kenji Kuba
Excitable Tissues and Central Nervous Physiology

Abstract

Ca2+-sensitive K+ currents involved in the slow afterhyperpolarization (a.h.p.) of an action potential of bullfrog sympathetic neurones were studied with a single-electrode voltage clamp method. The outward tail current (IAH) generated after the end of a depolarizing command pulse (from the holding potential of −60 mV to 0 mV, 5–20 ms in duration), mimicking an action potential, was separated into at least two exponential components (IAHf and IAHs). They were identified as K+ currents, since their reversal potentials were close to the K+ equilibrium potential and they were sensitive to external K+. The time constant of IAHf (tf; 44 ms at −60 mV) was decreased by membrane hyperpolarization from −40 to −80 mV, while that of IAHs (ts; 213 ms) remained constant. Removal of external Ca2+ or addition of Cd2+ significantly decreased the IAHs amplitude (As) andtf without a change ints and the IAHf amplitude (Af). On the other hand, increasing Ca2+ influx by applying repetitive command pulses enhanced both Af and As with negligible effects ontf andts, and produced a much slower component. Intracellular injection of EGTA reduced Af with no effect ontf, and increased As with a decreasedts. Both muscarine and (±)-tubocurarine, which reduced IAHs, hardly affected IAHf. These results indicate that a.h.p. is induced by the activation of two distinct Ca2+-dependent K+ channels, which differ in voltage sensitivity, Ca2+-dependence and pharmacology.

Key words

Ca2+-dependent K+ channel Afterhyperpolarization Bullfrog sympathetic neurone Single electrode voltage clamp 

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Kohichi Tanaka
    • 1
  • Kenji Kuba
    • 1
  1. 1.Department of PhysiologySaga Medical SchoolSagaJapan

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