Developmental regulation of the L-type calcium channel alpha(1C) subunit expression in heart

We used Northern analyses, RNase protection assays and immunoblot analyses to examine the relationship among developmental age of the heart, abundance of mRNA and L-type calcium channel alpha(1C) subunit protein, and to estab lish the size of the native protein in heart. Northern analysis, RNase prot ection assays, and immunoblots were used to study RNA and protein from rat heart of various ages. In fetal and adult ventricles there was a predominan t 8.3-kb transcript for the alpha(1C) subunit with no change in transcript size during development. RNase protection assays demonstrated a 2-fold incr ease in abundance of the DHP receptor message during postnatal development. Immunoblots identified a 240 kD protein, corresponding to the predicted mo lecular mass of the full length alpha(1C) subunit. No change in size of pro tein for the alpha(1C) subunit was observed at any developmental stage and there was no evidence for a truncated isoform. There was an approximate 2-f old increase in alpha(1C) subunit protein in ventricular homogenates during postnatal development. Thus, in the developing rat heart, alterations in c alcium channel properties during development appear to result neither from alternative splicing that produces a smaller transcript for the alpha(1C) s ubunit nor from expression of a truncated protein, but at least in part fro m transcriptionally-regulated expression of the 240 kDa polypeptide.