Quantitative Analysis of the Expression and Distribution of Calcium Channel α 1 Subunit mRNA in the Atria and Ventricles of the Rat Heart

Two distinct calcium currents are present in mammalian cardiac myocytes. Utilizing quantitative RT-PCR methods, we have analysed the expression patterns and abundance of four calcium channel α 1 subunit mRNAs in different regions of the rat heart and compared them to the known density of calcium currents recorded from rat atria. Our results show that CaV1.2 is the most abundant of the four α 1 subunit transcripts in the rat heart. The CaV1.2 message is more abundant in ventricle than in atria and does not vary in expression as a function of developmental age. CaV2.3, CaV3.1 and CaV3.2 mRNAs are 10–100 times less abundant than CaV1.2. Interestingly, CaV2.3, CaV3.1 and CaV3.2 are expressed in both atria and ventricle. The abundance of atrial CaV3.1 mRNA does not change significantly during development and remains high in older animals. In contrast, levels of atrial CaV3.2 mRNA are high in embryonic tissue and at 3- and 4-weeks postnatal but become undetectable at 5 weeks. Expression of atrial CaV2.3 mRNA is highest at 4-weeks postnatal and then declines gradually. We have previously documented that the LVA calcium current density is highest within 4–5 weeks after birth and then declines gradually reaching less than 30% of its maximal value at 12–14 weeks. The complex relationship between atrial LVA current density and the abundance of CaV2.3, CaV3.1 and CaV3.2 mRNA suggests that their contribution to the cardiac LVA current may vary as a function of postnatal age.