Details

Autor(en) / Beteiligte

• Sun, Xiao‐Ping
• Schlichter, Lyanne C.
• Stanley, Elis F.

Titel

Single-channel properties of BK-type calcium-activated potassium channels at a cholinergic presynaptic nerve terminal

Ist Teil von

• The Journal of physiology, 1999-08, Vol.518 (3), p.639-651

Ort / Verlag

Oxford, UK: The Physiological Society

Erscheinungsjahr

1999

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• A high-conductance calcium-activated potassium channel (BK K Ca ) was characterized at a cholinergic presynaptic nerve terminal using the calyx synapse isolated from the chick ciliary ganglion. The channel had a conductance of 210 pS in a 150 mM:150 mM K + gradient, was highly selective for K + over Na + , and was sensitive to block by external charybdotoxin or tetraethylammonium (TEA) and by internal Ba 2+ . At +60 mV it was activated by cytoplasmic calcium [Ca 2+ ] i with a K d of ≈0.5 μM and a Hill coefficient of ≈2.0. At 10 μM [Ca 2+ ] i the channel was 50 % activated ( V ½ ) at -8.0 mV with a voltage dependence (Boltzmann slope-factor) of 32.7 mV. The V ½ values hyperpolarized with an increase in [Ca 2+ ] i while the slope factors decreased. There were no overt differences in conductance or [Ca 2+ ] i sensitivity between BK channels from the transmitter release face and the non-release face. Open and closed times were fitted by two and three exponentials, respectively. The slow time constants were strongly affected by both [Ca 2+ ] i and membrane potential changes. In cell-attached patch recordings BK channel opening was enhanced by a prepulse permissive for calcium influx through the patch, suggesting that the channel can be activated by calcium ion influx through neighbouring calcium channels. The properties of the presynaptic BK channel are well suited for rapid activation during the presynaptic depolarization and Ca 2+ influx that are associated with transmitter release. This channel may play an important role in terminating release by rapid repolarization of the action potential.