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The Journal of Neurophysiology Vol. 84 No. 4 October 2000, pp. 2026-2034
Copyright ©2000 by the American Physiological Society
-Adrenergic Receptor-Mediated
Activation of Hyperpolarization-Activated Cation Channels in Rat
Cerebellar Basket Cells
Laboratory of Molecular Neurobiology, Mitsubishi Kasei Institute of Life Sciences and CREST, JST (Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation), Tokyo 194-8511, Japan
Saitow, Fumihito and
Shiro Konishi.
Excitability Increase Induced by
-Adrenergic Receptor-Mediated
Activation of Hyperpolarization-Activated Cation Channels in Rat
Cerebellar Basket Cells. J. Neurophysiol. 84: 2026-2034, 2000. In the preceding paper, we showed
that norepinephrine (NE) enhances the spontaneous spike firings in
cerebellar interneurons, basket cells (BCs), resulting in an
increase in the frequency of BC-spike-triggered inhibitory postsynaptic
currents (IPSCs) in Purkinje cells (PCs), and that the effects of
NE on GABAergic BCs are mediated by
2-adrenergic receptors. This study aimed to
further examine the ionic mechanism underlying the
-adrenoceptor-mediated facilitation of GABAergic transmission at the
BC-PC synapses. Using cerebellar slices obtained from 15- to 21-day-old
rats and whole cell recordings, we investigated ionic currents in the
BCs and the effects of the
-agonist isoproterenol (ISP) as well as forskolin on the BC excitability. Hyperpolarizing voltage steps from a
holding potential of
50 mV elicited a hyperpolarization-activated inward current, Ih, in the BC. This
current exhibited voltage-dependent activation that was accelerated by
strong hyperpolarization, displaying two time constants, 84 ± 6 and 310 ± 40 ms, at
100 mV, and was inhibited by 20 µM
ZD7288. ISP and forskolin, both at 20 µM, enhanced Ih by shifting the activation curve by
5.9 and 9.3 mV toward positive voltages, respectively. Under the
current-clamp mode, ISP produced a depolarization of 7 ± 3 mV in
BCs and reduced their input resistance to 74 ± 6%. ISP and a
cAMP analogue, Rp-cAMP-S, increased the frequency of spontaneous spikes
recorded from BCs using the cell-attached mode. The
Ih inhibitor ZD7288 decreased the BC
spike frequency and abolished the ISP-induced increase in spike
discharges. The results suggest that NE depolarizes the BCs through
-adrenoceptor-mediated cAMP formation linking it to activation of
Ih, which is, at least in part,
involved in noradrenergic afferent-mediated facilitation of GABAergic
synaptic activity at BC-PC connections in the rat cerebellum.
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