A novel first exon for the human cardiac L-type calcium channel has been discovered, bringing to three the number of transcripts found with different 5' ends, each likely regulated by its own promoter. Two of these transcripts are of critical significance, since they account for the majority of transcripts in heart and smooth muscle, respectively. This grant hypothesizes that differential expression of these two principal transcripts in heart and in vascular and visceral smooth muscle not only generates significant differences in channel activity, sensitivity to protein kinase C, and steady-state inactivation but also greater ability to separately regulate expression in the three tissue types. Adrenergic agents are known to transcriptionally upregulate and then downregulate this channel in heart, but equivalent information is lacking for smooth muscle. This grant will test three specific hypotheses: 1) that heterologous expression of the different transcripts in Xenopus oocytes and human cells results in Ca currents with different amplitude, kinetics, open probability, sensitivity to protein kinase C and steady state inactivation properties; 2) that the two principal transcripts are differentially affected in heart and smooth muscle by adrenergic agents; 3) and that there are heart-specific transcription factors that bind to response elements in the heart promoter for the channel, whereas most smooth muscle expression is driven by other transcription factors that bind to response elements in the other principal channel promoter. The results will determine how the different N-termini affect channel properties and how the different transcripts are differentially regulated in vascular smooth muscle as opposed to heart and visceral smooth muscle. They could suggest new targets for pharmaceutical intervention in disorders involving alterations in expression of L-type Ca channels, such as hypertension.

R01HL073097

2003-12-20

2008-11-30