The Ca2+-sensitive K+-currents underlying the slow afterhyperpolarization of bullfrog sympathetic neurones (original) (raw)
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 (t f; 44 ms at −60 mV) was decreased by membrane hyperpolarization from −40 to −80 mV, while that of IAHs (t s; 213 ms) remained constant. Removal of external Ca2+ or addition of Cd2+ significantly decreased the IAHs amplitude (As) and_t_ f without a change in_t_ s 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 on_t_ f and_t_ s, and produced a much slower component. Intracellular injection of EGTA reduced Af with no effect on_t_ f, and increased As with a decreased_t_ s. 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.
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- Kohichi Tanaka
Present address: Department of Neurochemistry, Brain Research Institute, Niigata University, 951, Niigata, Japan
Authors and Affiliations
- Department of Physiology, Saga Medical School, 840-01, Saga, Japan
Kohichi Tanaka & Kenji Kuba
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- Kohichi Tanaka
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Tanaka, K., Kuba, K. The Ca2+-sensitive K+-currents underlying the slow afterhyperpolarization of bullfrog sympathetic neurones.Pflugers Arch. 410, 234–242 (1987). https://doi.org/10.1007/BF00580271
- Received: 20 October 1986
- Revised: 24 May 1987
- Accepted: 30 May 1987
- Issue Date: October 1987
- DOI: https://doi.org/10.1007/BF00580271