A 2-MOTIF ISOFORM OF THE MAJOR CALCIUM-CHANNEL SUBUNIT IN SKELETAL-MUSCLE

Evidence is presented that two isoforms of the voltage-dependent, dihydropyridine-sensitive calcium channel alpha-1 subunit are present in newborn and adult skeletal muscle and that expression of these isoforms is developmentally regulated. A voltage-dependent calcium channel alpha-1 cDNA from newborn muscle was cloned and found to be identical to that published from the adult, except that it was 2 kb shorter owing to an internal deletion. Nucleotide sequences, Northern blots, reverse-transcriptase PCR experiments, and sequencing of the PCR product confirmed that a segment corresponding to the inner two repeats of the structural prototype four homologous motifs is missing from the immature isoform. Immunological studies using antisera raised against synthetic peptides that correspond to sequences in the two isoforms show that the abbreviated transcript is predominant in newborn muscle, whereas the four-repeat isoform is the major species in the adult.