Antisense oligonucleotides against rat brain α(1E) DNA and its atrial homologue decrease T-type calcium current in atrial myocytes

Low voltage-activated, or T-type, calcium currents are important regulators of neuronal and muscle excitability, secretion, and possibly cell growth and differentiation. The gene (or genes) coding for the pore-forming subunit of low voltage-activated channel proteins has not been unequivocally identified. We have used reverse transcription–PCR to identify partial clones from rat atrial myocytes that share high homology with a member of the E class of calcium channel genes. Antisense oligonucleotides targeting one of these partial clones (raE1) specifically block the increase in T-current density that normally results when atrial myocytes are treated with insulin-like growth factor 1 (IGF-1). Antisense oligonucleotides targeting portions of the neuronal rat α(1E) sequence, which are not part of the clones detected in atrial tissue, also block the IGF-1-induced increase in T-current, suggesting that the high homology to α(1E) seen in the partial clone may be present in the complete atrial sequence. The basal T-current expressed in these cells is also blocked by antisense oligonucleotides, which is consistent with the notion that IGF-1 up-regulates the same gene that encodes the basal current. These results support the hypothesis that a member of the E class of calcium channel genes encodes a low voltage-activated calcium channel in atrial myocytes.