Rk. Cloues et al., BETA-ADRENERGIC STIMULATION SELECTIVELY INHIBITS LONG-LASTING L-TYPE CALCIUM-CHANNEL FACILITATION IN HIPPOCAMPAL PYRAMIDAL NEURONS, The Journal of neuroscience, 17(17), 1997, pp. 6493-6503
L-type calcium channels are abundant in hippocampal pyramidal neurons
and are highly clustered at the base of the major dendrites. However,
little is known of their function in these neurons. Single-channel rec
ording using a low concentration of permeant ion reveals a long-lastin
g facilitation of L-type channel activity that is induced by a depolar
izing prepulse or a train of action potential waveforms. This facilita
tion exhibits a slow rise, peaking 0.5-1 sec after the train and decay
ing over several seconds. We have termed this behavior ''delayed facil
itation,'' because of the slow onset. Delayed facilitation results fro
m an increase in opening frequency and the recruitment of longer durat
ion openings. This behavior is observed at all membrane potentials bet
ween -20 and -60 mV, with the induction and magnitude of facilitation
being insensitive to voltage. beta-Adrenergic receptor activation bloc
ks induction of delayed facilitation but does not significantly affect
normal L-type channel activity. Delayed facilitation of L-type calciu
m channels provides a prolonged source of calcium entry at negative me
mbrane potentials, This behavior may underlie calcium-dependent events
that are inhibited by beta-adrenergic receptor activation, such as th
e slow afterhyperpolarization in hippocampal neurons.