Electrophysiological and Pharmacological Characterization of a Mammalian
Shaw Channel Expressed in NIH 3T3 Fibroblasts.
Kanemasa, T., L. Gan, T.M. Perney, L.Y. Wang, L.K. Kaczmarek.
Depts. of Pharmacology and Cellular and Molecular Physiology, Yale School
of Medicine, 333 Cedar St., New Haven, CT 06520.
APStracts 2:0021N, 1995.
SUMMARY AND CONCLUSIONS
1) The Shaw -like voltage-activated potassium channel Kv3.1 is expressed in
neurons that generate rapid trains of action potentials. By expressing this
channel in a mammalian cell line and, by simulating its activation, we have
tested the potential role of this channel in action potential repolarization.
2) NIH 3T3 fibroblasts were stably transfected with Kv3.1 DNA. Currents
recorded in these cells had a threshold of activation at approximately -10 mV,
showed little inactivation, and were very sensitive to blockade by 4-
aminopyridine (4-AP) and tetraethylammonium (TEA). 3) Kv3.1 currents activated
rapidly at the onset of depolarizing voltage pulses. After an initial rapid
phase of activation, which could be fit by a n 4 Hodgkin- Huxley model,
Kv3.1 currents expressed in fibroblasts had a second slower phase of
activation, and, in some cells, a slower phase of partial inactivation, both
of which could be fit with modified n 4 p models. 4) Cell-attached single
channel recordings indicated that the Kv3.1 channel displays two gating
behaviors, a short open time pattern, which occurs only at the onset of
depolarization, and a long open time pattern, which predominates during
prolonged depolarizations. 5) The amplitude of Kv3.1 currents, and the
probability of channel openings, was reduced by a phorbol ester activator of
protein kinase C, and the action of this agent was blocked by preincubation
with the protein kinase inhibitor H7. In contrast, the effects of dioctanoyl
glycerol, which also attenuated the currents, could not be completely blocked
by H7 suggesting that diacylglycerols may act on the channel by a kinase-
independent pathway. 6) Incorporation of a current with the kinetics and
voltage-dependence of Kv3.1 currents into a model cell with a sustained inward
current showed that, in contrast to other delayed rectifier currents such as
the Shaker- like Kv1.1 and Kv1.6 channels, the levels of expression of Kv3.1
currents could be varied over a wide range without attenuation of action
potential height. Our results suggest that the Kv3.1 channel may provide
rapidly-firing neurons with a high safety factor for impulse propagation.
Received 20 January 1994; accepted in final form 10 March 1995.
APS Manuscript Number J48-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.