TY - JOUR
T1 - Characterization of an apamin-sensitive potassium current in suprachiasmatic nucleus neurons
AU - Teshima, K.
AU - Kim, S. H.
AU - Allen, C. N.
PY - 2003/8/4
Y1 - 2003/8/4
N2 - In neurons of the suprachiasmatic nucleus, spike frequency adaptation and membrane afterhyperpolarization occur during a train of action potentials. Extracellular Ca2+ may regulate neuronal excitability by several mechanisms, including activation of small conductance and large conductance Ca2+-activated K+ channels. The overall goal of this study was to examine the role of Ca2+-activated K+ currents in individual suprachiasmatic nucleus neurons. To this end, we used the nystatin-perforated patch technique to record currents from suprachiasmatic nucleus neurons. Iberiotoxin and tetraethylammonium, antagonists of large conductance Ca2+-activated K+ channels, had no effect on the membrane afterhyperpolarization. However, antagonists of small conductance Ca2+-activated K+ channels, apamin and d-tubocurarine, reduced the amplitude of the membrane afterhyperpolarization and inhibited the spike frequency adaptation that occurred during a train of action potentials. Although there was no significant difference in membrane AHP between different portions of the circadian day, apamin and d-tubocurarine increased the spontaneous firing frequency of suprachiasmatic nucleus neurons during the daytime. In voltage-clamp mode, membrane depolarization-activated currents were followed by an outward tail current reversing near the K+ equilibrium potential. The tail current decayed with a time constant of 220 ms at +20 mV and 149 ms at -40 mV. Apamin irreversibly and d-tubocurarine reversibly inhibited the tail current. The tail current amplitude was also reduced by the GABAA receptor antagonist, bicuculline methiodide, while picrotoxin (another GABAA receptor antagonist) was without effect. Removal of extracellular Ca2+ or the addition of Cd2+ reversibly inhibited the tail current. These results indicate that apamin- and d-tubocurarine-sensitive small conductance Ca2+-activated K+ channels have a modulatory function on the action potential firing frequency as well as the membrane afterhyperpolarization that follows a train of action potentials in suprachiasmatic nucleus neurons. Importantly, our data also indicate that a portion of the effects of bicuculline methiodide on suprachiasmatic nucleus neurons may be mediated by inhibition of small conductance Ca2+-activated K+ channels.
AB - In neurons of the suprachiasmatic nucleus, spike frequency adaptation and membrane afterhyperpolarization occur during a train of action potentials. Extracellular Ca2+ may regulate neuronal excitability by several mechanisms, including activation of small conductance and large conductance Ca2+-activated K+ channels. The overall goal of this study was to examine the role of Ca2+-activated K+ currents in individual suprachiasmatic nucleus neurons. To this end, we used the nystatin-perforated patch technique to record currents from suprachiasmatic nucleus neurons. Iberiotoxin and tetraethylammonium, antagonists of large conductance Ca2+-activated K+ channels, had no effect on the membrane afterhyperpolarization. However, antagonists of small conductance Ca2+-activated K+ channels, apamin and d-tubocurarine, reduced the amplitude of the membrane afterhyperpolarization and inhibited the spike frequency adaptation that occurred during a train of action potentials. Although there was no significant difference in membrane AHP between different portions of the circadian day, apamin and d-tubocurarine increased the spontaneous firing frequency of suprachiasmatic nucleus neurons during the daytime. In voltage-clamp mode, membrane depolarization-activated currents were followed by an outward tail current reversing near the K+ equilibrium potential. The tail current decayed with a time constant of 220 ms at +20 mV and 149 ms at -40 mV. Apamin irreversibly and d-tubocurarine reversibly inhibited the tail current. The tail current amplitude was also reduced by the GABAA receptor antagonist, bicuculline methiodide, while picrotoxin (another GABAA receptor antagonist) was without effect. Removal of extracellular Ca2+ or the addition of Cd2+ reversibly inhibited the tail current. These results indicate that apamin- and d-tubocurarine-sensitive small conductance Ca2+-activated K+ channels have a modulatory function on the action potential firing frequency as well as the membrane afterhyperpolarization that follows a train of action potentials in suprachiasmatic nucleus neurons. Importantly, our data also indicate that a portion of the effects of bicuculline methiodide on suprachiasmatic nucleus neurons may be mediated by inhibition of small conductance Ca2+-activated K+ channels.
KW - Action potential
KW - Apamin
KW - Calcium-activated potassium channel
KW - Circadian rhythm
KW - Membrane afterhyperpolarization
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U2 - 10.1016/S0306-4522(03)00270-7
DO - 10.1016/S0306-4522(03)00270-7
M3 - Article
C2 - 12849741
AN - SCOPUS:0037828634
SN - 0306-4522
VL - 120
SP - 65
EP - 73
JO - Neuroscience
JF - Neuroscience
IS - 1
ER -