Upregulation of L-Type Ca2+ Channels in Mesenteric and Skeletal Arteries of SHR

An increased Ca2+ influx attributed to dihydropyridine-sensitive L-type Ca2+ channels has been demonstrated in mesenteric vascular smooth muscle cells of spontaneously hypertensive rats (SHR). This study examined whether an upregulation of the pore-forming &agr;1C subunit of the L-type Ca2+ channel underlies this ionic defect. With the use of mesenteric arcade arteries from 12- to 16-week-old SHR and normotensive Wistar Kyoto (WKY) rats, reverse transcriptase–polymerase chain reaction demonstrated an increased level of amplified cDNA corresponding to the &agr;1C subunit mRNA in the SHR arteries. Western blots confirmed that the increased mRNA expression was associated with a 3.4-fold increase in the immunoreactive signal of the &agr;1C subunit protein in SHR compared with WKY mesenteric arteries, and immunocytochemistry confirmed this abnormality at the single-cell level. Finally, isolated mesenteric arteries from SHR were highly reactive to Bay K8644 and developed anomalous Ca2+-dependent tone, suggesting a functional role for &agr;1C subunit upregulation in vascular hyperreactivity. To determine if these Ca2+ channel abnormalities extended to the SHR skeletal muscle bed, we repeated a similar series of studies in WKY and SHR hind limb arteries. Skeletal muscle arteries from SHR also expressed higher levels of &agr;1C subunit mRNA and protein than WKY arteries and developed anomalous Ca2+-dependent tone attributed to L-type Ca2+ channels. Our data provide the first evidence that the &agr;1C subunit mRNA and protein are upregulated in SHR arteries and that the increased numbers of L-type Ca2+ channel pores are associated with the generation of abnormal vascular tone.