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The vasculature of the adult spontaneously hypertensive rat (SHR) is known to express more functional L-type Ca channels than the vasculature of normotensive Wistar Kyoto (WKY) rats, but it is not known which CaV1.2 channel isoform is upregulated.Western blots and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) were used to compare the expression levels of CaV1.2 channel protein and message in selected tissues of adult SHR and WKY rats.The results indicate overexpression in SHR vasculature specifically of the short exon 1b-encoded amino terminus CaV1.2 isoform. Brain and visceral smooth muscle expressing the same isoform were not similarly affected. Differences in message levels are insufficient to account for the differences in isoform-specific protein levels.We conclude that SHR vasculature must regulate the channel postranscriptionally. Further experiments will be required to determine whether this involves translation of protein from exon 1b-specific transcripts more efficiently, posttranslational chaperoning to the surface membrane more efficiently, or selective degradation of the short amino terminus form of the protein more slowly than in WKY vasculature.