Tissue distribution of a human Ca v 1.2 alpha1 subunit splice variant with a 75 bp insertion.
Mesenchymal stem cells from human bone marrow (MSC) express mRNA encoding the L-type Ca2+ channel Ca v 1.2 alpha1 subunit (alpha(1)1.2). We now describe a splice variant including an alternative exon of 75 bp in the region between exons 9 and 10, which we identified in MSC by semi-quantitative RT-PCR. With primers specific for variants including (+9*) or excluding the 75 bp insertion (-9*), we found comparable mRNA expression patterns in MSC and in primary cultures of related connective tissue cells (chondrocytes, osteoblasts and fibroblasts). Since culture conditions might have altered variant expression, we investigated mRNA levels in various native human tissue samples (cartilage, bone, fat, liver, kidney, aorta, bladder, cardiac ventricle and atrium, CNS). We found highest levels of the +9* variant in aorta, containing smooth muscle and connective tissue cells, but the variant was expressed in all tissues. We therefore hypothesized that broad expression of +9* might be linked to the presence of vasculature and/or connective tissue structures, rather than to tissue-specific parenchymal cells (e.g. cardiomyocytes). To test this hypothesis we separated human atrium into a cardiomyocyte-enriched fraction and a cardiomyocyte-depleted fraction. RT-PCR demonstrated significantly larger levels of the +9* variant in the non-cardiomyocyte fraction. The result was even more clear in single cell RT-PCR experiments, where the +9* variant was undetectable in cardiomyocytes but present in non-cardiomyocytes. We conclude that the +9* variant is present in all human tissues investigated so far, and suggest that expression in human atrium is associated with vascular smooth muscle and/or connective tissue cells.
Graf
Eva M
EM
Institut für Pharmakologie und Toxikologie, Medizinische Fakultät Carl Gustav Carus der TU Dresden, Fetscherstr. 74, D-01307 Dresden, Germany. eva.graf@mailbox.tu-dresden.de
Bock
Manja
M
Heubach
Jürgen F
JF
Zahanich
Ihor
I
Boxberger
Sabine
S
Richter
Wiltrud
W
Schultz
Jobst H
JH
Ravens
Ursula
U
D000328:Adult; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001011:Aorta / Q000378:metabolism; D001483:Base Sequence; D001853:Bone Marrow / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D003238:Connective Tissue / Q000378:metabolism; D005091:Exons / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008297:Male; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D012333:RNA, Messenger; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution
D020746:Calcium Channels, L-Type; C419385:L-type calcium channel alpha(1C); D012333:RNA, Messenger