A FAMILY OF DELAYED RECTIFIER KV1 CDNAS SHOWING CELL-TYPE-SPECIFIC EXPRESSION IN THE SQUID STELLATE GANGLION GIANT FIBER LOBE COMPLEX

Squid giant axons are formed by giant fiber lobe (GFL) neurons of the stellate ganglion (SG). Other large motoneurons in the SG form a paral lel system. A small family of cDNAs (SqKv1A-D) encoding Kv1 alpha-subu nits was identified in a squid (Loligo opalescens) SG/GFL library. Mem bers have distinct 5' untranslated regions (UTRs) and initial coding r egions, but beyond a certain point (nucleotide 34 of SqKv1A) only nine differences exist. 3' UTRs are identical. Predicted alpha-subunits ar e nearly identical, and only the N termini differ significantly, prima rily in length. RNase protection assays that use RNA isolated from spe cific SG regions show that SqKv1A mRNA is expressed prominently in the GFL but not in the SG proper. SqKv1B yields the opposite pattern. SqK v1D also is expressed only in the SG. SqKv1C expression was not detect able. in situ hybridizations confirm these results and reveal that SqK v1B mRNA is abundant in many large neurons of the SG, whereas SqKv1D e xpression is limited to small isolated clusters of neurons. SqKv1A and B are thus the predominant Kv1 mRNAs in the SG/GFL complex. Activatio n properties of SqKv1A and B channels expressed in oocytes are very si milar to one another and compare favorably with properties of native d elayed rectifier channels in GFL neurons and large SG neurons, The Ky1 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.