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Journal of Neuroscience, Vol 6, 814-822, Copyright © 1986 by Society for Neuroscience
Multiple components of delayed potassium current in peptidergic neurons of Aplysia: modulation by an activator of adenylate cyclase
JA Strong and LK Kaczmarek
The neurosecretory bag cell neurons of the mollusk, Aplysia, control
egg-laying behavior in the animal. In these cells, elevation of cAMP
greatly enhances the height and width of action potentials. A similar
enhancement of action potentials is seen during the bag cell
afterdischarge, a 30 min period of repetitive activity that may be
triggered by peptides from the reproductive tract or by brief extracellular
stimulation. The enhancement of action potentials during an afterdischarge
is well correlated with the observed elevations of cAMP. In the present
study, we have examined the effects of forskolin (an activator of adenylate
cyclase) and theophylline (a phosphodiesterase inhibitor) on the delayed
outward currents that are likely to control repolarization of the action
potential. Isolated bag cell neurons, maintained in primary culture, were
studied with a whole- cell patch clamp technique. High intracellular
concentrations of EGTA were used to block potassium current activated by
calcium entry. Analysis of the remaining voltage-dependent delayed outward
current revealed two major components, which could be separated on the
basis of their different kinetic properties. Both currents (IK1 and IK2)
were carried by potassium. IK1, which did not inactivate during 100 msec
depolarizations, was reduced in amplitude by application of forskolin and
theophylline. Ik2, a current defined by its faster kinetic properties,
partially inactivated during 100 msec depolarizations. This inactivation
was markedly speeded by application of forskolin and theophylline. It is
suggested that such changes in outward current in response to cAMP could
explain the enhancement of spike width seen during an afterdischarge in
vivo.
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