Consists of the slo H13 cDNA expressed under the control of the complete slo regulatory region. SV40 transcription termination and polyadenylation sites are present downstream of the cDNA. The transcript produced begins with alternative exon C2 and includes alternative exons 1a, 2b, 3a and 4bf. At splice site 5, the alternative exon is skipped ("splice pattern 5b"). This isoform is naturally found in muscle.