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Properties and functions of calcium‐activated K + channels in small neurones of rat dorsal root ganglion studied in a thin slice preparation
Author(s) -
Scholz Andreas,
Gruß Marco,
Vogel Werner
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.055by.x
Subject(s) - chemistry , dorsal root ganglion , conductance , iberiotoxin , depolarization , tetraethylammonium , biophysics , repolarization , charybdotoxin , hyperpolarization (physics) , patch clamp , membrane potential , electrophysiology , calcium , anatomy , potassium , neuroscience , biochemistry , stereochemistry , dorsum , physics , biology , organic chemistry , receptor , condensed matter physics , nuclear magnetic resonance spectroscopy
1 Properties, kinetics and functions of large conductance calcium‐activated K + channels (BK Ca ) were investigated by the patch‐clamp technique in small neurones (Aδ‐ and C‐type) of a dorsal root ganglion (DRG) thin slice preparation without enzymatic treatment. 2 Unitary conductance of BK Ca channels measured in symmetrical high K + solutions (155 m m ) was 200 pS for inward currents, and chord conductance in control solution was 72 pS. Potentials of half‐maximum activation ( V 1/2 ) of the channels were linearly shifted by 43 mV per log 10 [Ca 2+ ] i unit (pCa) in the range of −28 mV (pCa 4) to +100 mV (pCa 7). Open probabilities increased e‐times per 15–32 mV depolarization of potential. 3 In mean open probability, fast changes with time were mainly observed at pCa > 6 and at potentials > +20 mV, without obvious changes in the experimental conditions. 4 BK Ca channels were half‐maximally blocked by 0.4 m m TEA, measured by apparent amplitude reductions. They were completely blocked by 100 n m charybdotoxin and 50 n m iberiotoxin by reduction of open probability. 5 Two subtypes of small DRG neurones could be distinguished by the presence (type I) or absence (type II) of BK Ca channels. In addition, less than 10 % of small neurones showed fast (∼135 V s −1 ) and short (∼0.8 ms) action potentials (AP). 6 The main functions of BK Ca channels were found to be shortening of AP duration, increasing of the speed of repolarization and contribution to the fast after‐hyperpolarization. As a consequence, BK Ca channels may reduce the amount of calcium entering a neurone during an AP. 7 BK Ca channel currents suppressed a subsequent AP and prolonged the refractory period, which might lead to a reduced repetitive activity. We suggest that the BK Ca current is a possible mechanism of the reported conduction failure during repetitive stimulation in DRG neurones.