IDENTIFICATION OF CA2+ ACTIVATED K+ CHANNEL SPLICE VARIANTS AND THEIRDISTRIBUTION IN THE TURTLE COCHLEA

Turtle auditory-hair cells are frequency-tuned by the activity of calc ium-activated potassium (K-Ca) channels, a cell's characteristic frequ ency being determined by the K-Ca channel density and kinetics which b oth vary systematically along the cochlea. As a first step towards ide ntifying the source of K-Ca channel variation, we have isolated, by re verse-transcription polymerase chain reaction on dissociated hair cell s, the main cDNAs homologous to the slo gene which encodes the channel 's alpha-subunit. A total of six alternatively spliced variants were i dentified, the smallest of which is 94% identical to a mouse Slo seque nce. Variation occurs by insertion of exons at only two splice sites, two of these exons encoding novel 31- and 61-amino acid sequences. As we were unable to detect splicing at other potential sites, we infer t hat the six variants correspond to naturally occurring combinations. T he spatial distribution of the variants, defined by isolating hair cel ls from different regions of the cochlea, indicated that some isoforms were non-uniformly distributed. Those containing large inserts in the first splice site were notably absent from the highest-frequency regi on. We suggest that alternative splicing of the slo gene may contribut e to variation in K-Ca channel properties.