Quantitative analysis of the expression and distribution of calcium channel α1 subunit mRNA in the atria and ventricles of the rat heart

J. K. LARSEN, J. W. MITCHELL AND P. M. BEST. Quantitative Analysis of the Expression and Distribution of Calcium Channel al Subunit mRNA in the Atria and Ventricles of the Rat Heart. journal of Molecular and Cellular Cardiology (2002) 34. 519-532. 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 al 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 Ca(v)1.2 is the most abundant of the four al subunit transcripts in the rat heart. The Ca(v)1.2 message is more abundant in ventricle than in atria and does not vary in expression as a function of developmental age. Ca(v)2.3, Ca(v)3.1 and Ca(v)3.2 mRNAs are 10-100 times less abundant than Ca(v)1.2. Interestingly, Ca(v)2.3, Ca(v)3.1 and Ca(v)3.2 are expressed in both atria and ventricle. The abundance of atrial Ca(v)3.1 mRNA does not change significantly during development and remains high in older animals. In contrast, levels of atrial Ca(v)3.2 mRNA are high in embryonic tissue and at 3- and 4-weeks postnatal but become undetectable at 5 weeks. Expression of atrial Ca(v)2.3 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 Ca(v)2.3, Ca(v)3.1 and Ca(v)3.2 mRNA suggests that their contribution to the cardiac LVA current may vary as a function of postnatal age. (C) 2002 Elsevier Science Ltd. All rights reserved.