TWO TEMPORALLY OVERLAPPING "DELAYED-RECTIFIERS" DETERMINE THE VOLTAGE-
DEPENDENT POTASSIUM CURRENT PHENOTYPE IN CULTURED HIPPOCAMPAL INTERNEURONS.
Chikwendu, Adaora & Chris J. McBain.
Unit on Cellular and Synaptic Physiology, Lab. of Cellular and Molecular
Neurophysiology, Rm. 5A72, Bldg. 49, NICHD-LCMN, 49 Convent Drive, Bethesda MD
APStracts 3:0072N, 1996.
SUMMARY AND CONCLUSIONS
1. Whole-cell voltage clamp recordings were used to characterize the calcium-
independent "delayed-rectifier" potassium currents of GABA-positive st.
radiatum - lacunosum - moleculare interneurons in primary culture derived from
neonate rats (P5- P7). 2. Two distinct current phenotypes were observed, which
we termed "sustained" and "slowly-inactivating". Despite possessing similar
voltage-dependent activation properties, currents differed in their time-
dependent inactivation properties and their kinetics of activation and
deactivation. The phenotypes of the observed currents did not change during
the time in vitro. The total current phenotype observed in any cell likely
resulted from the temporal overlap of the two current components expressed in
different relative proportions. 3. Externally applied 4AP selectively blocked
the slowly-inactivating current component, by a use-dependent, but voltage-
independent mechanism, suggesting that channel activation is required for 4AP
to interact with its binding site. In contrast, the sustained current
component was unaffected by 4AP. 4. Both the slowly-inactivating and sustained
current phenotypes were sensitive to externally applied TEA. The IC 50 of
block by TEA was lower in cells expressing predominantly the sustained current
component. 5. Currents recorded in the presence of internally applied TEA were
of a slowly-inactivating phenotype, suggesting that [TEA] i preferentially
blocked the sustained current component. 6 . When test pulses were preceded by
a prepulse to -100mV, a transient A-type current component was observed but in
contrast to pyramidal neurons and other interneuron types, this transient
current contributed only a minor component to the total initial peak current.
7. In conclusion, two distinct, temporally overlapping potassium current
phenotypes were observed on st. L-M interneurons. The overall phenotype was
determined by the relative proportion of each current component. The absence
of a prominent transient current suggests that the two delayed-rectifier
currents play a critical role in determining the firing characteristics of
Received 2 February 1995; accepted in final form 10 April 1996.
APS Manuscript Number J88-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96