Volume 17, Number 13,
Issue of July 1, 1997
pp. 5070-5079
Copyright ©1997 Society for Neuroscience
A Family of Delayed Rectifier Kv1 cDNAs Showing
Cell Type-Specific Expression in the Squid Stellate
Ganglion/Giant Fiber Lobe Complex
Received Feb. 7, 1997; revised April 16, 1997; accepted April 21, 1997.
Joshua J. C. Rosenthal,
Taylor I. Liu, and
William F. Gilly
Hopkins Marine Station, Department of Biological Sciences, Stanford
University, Pacific Grove, California 93950
Squid giant axons are formed by giant fiber lobe (GFL) neurons of
the stellate ganglion (SG). Other large motoneurons in the SG form a
parallel system. A small family of cDNAs (SqKv1A-D) encoding Kv1
-subunits was identified in a squid (Loligo
opalescens) SG/GFL library. Members have distinct 5
untranslated regions (UTRs) and initial coding regions, but beyond a
certain point (nucleotide 34 of SqKv1A) only nine differences exist. 3
UTRs are identical. Predicted
-subunits are nearly identical, and only the N termini differ significantly, primarily in length. RNase
protection assays that use RNA isolated from specific SG regions show
that SqKv1A mRNA is expressed prominently in the GFL but not in the SG
proper. SqKv1B yields the opposite pattern. SqKv1D also is expressed
only in the SG. SqKv1C expression was not detectable. In
situ hybridizations confirm these results and reveal that
SqKv1B mRNA is abundant in many large neurons of the SG, whereas SqKv1D
expression is limited to small isolated clusters of neurons. SqKv1A and
B are thus the predominant Kv1 mRNAs in the SG/GFL complex. Activation
properties of SqKv1A and B channels expressed in oocytes are very
similar to one another and compare favorably with properties of native
delayed rectifier channels in GFL neurons and large SG neurons. The Kv1
complement in these squid neurons thus seems to be relatively simple.
Several differences exist between cloned and native channels, however,
and may reflect differences in the cellular environments of oocytes and
neurons.
Key words:
squid giant axon;
cloning;
Kv1 genes;
potassium channels;
expression;
alternative splicing