Pathophysiological significance of T-type Ca2+ channels:: Expression of T-type Ca2+ channels in fetal and diseased heart

Re-expression of fetal genes has been considered to underlie ionic remodeling in diseased heart. T-type Ca2+ channels have been reported to be functionally expressed in embryonic hearts. In this review, we summarize developmental changes of T-type Ca2+ channels in mouse ventricles from 9.5 days postcoitum (dpc) to adulthood, using patch clamp and quantitative PCR. In addition, we introduced T-type Ca2+ channel expression in hypertrophied ventricles caused by myocardial infarction (MI) and aortic banding (AOB). Substantial T-type Ca2+ channel current was recorded at both 9.5 and 18 dpc. The currents were inhibited by Ni2+ at low concentrations. The current was not detectable in the adult stage. Ca(nu)3.2 (alpha(1H)) mRNA is expressed dominantly at both 9.5 and 18 dpc. Ca(nu)3.1 (alpha(1G)) increases from 9.5 to 18 dpc, but remains at low level compared with Ca(nu)3.2. In contrast, Ca(nu)3.1 is greater than Ca(nu)3.2 at the adult stage. In MI, Ca(nu)3.1 mRNA correlates negatively with brain natriuretic peptide (BNP) mRNA, whereas Ca(nu)3.2 mRNA correlates positively with BNP mRNA. In AOB, these correlations are weak. We also analyzed the neuron-restrictive silencer factor (NRSF) in these hearts because it is the suppressor of transcription of the fetal cardiac gene program. The negative correlation between NRSF and BNP was stronger in MI than in AOB. Our findings show that Ca(nu)3.2 underlies the functional T-type Ca2+ channel in embryonic heart and suggest that NRSF may regulate Ca(nu)3.2 expression in diseased hearts.