High blood pressure upregulates arterial L-type Ca2+ channels: is membrane depolarization the signal?

Long-lasting Ca2+ (Ca(L)) channels of the Ca(v)1.2 gene family contribute to the pathogenesis of abnormal arterial tone in hypertension. The physiological stimulus that enhances Ca(L) channel current in the vascular smooth muscle cells (VSMCs) remains unknown. The present study investigated if high blood pressure triggers an upregulation of vascular Ca(L) channel protein. Rat aortae were banded between the origins of the left renal (LR) and right renal (RR) arteries to selectively elevate blood pressure in the proximal RR arteries. After 2 days, the immunoreactivity on Western blots corresponding to the pore-forming alpha1C subunit of the Ca(L) channel was increased 3.25-fold in RR compared with LR arteries. This finding persisted at 28 days and was associated with abnormal Ca2+-dependent tone and higher Ca(L) currents in the VSMCs exposed to high pressure. Based on microelectrode studies indicating that RR arteries were depolarized compared with LR arteries, further studies examined if membrane depolarization, an inherent response of VSMCs to high blood pressure, increased alpha1C expression. Isolated rat renal arteries were cultured for 2 days in low K+ (4 mmol/L) or depolarizing high K+ (30 mmol/L) media. Arteries preconditioned in high K+ showed a 5.47-fold increase in alpha1C expression, enhanced Ca(L) channel current, and elevated Ca2+-dependent tone. These findings provide the first direct evidence that high blood pressure upregulates the Ca(L) channel alpha1C subunit in VSMCs in vivo and suggest that membrane depolarization is a potential signal involved in this interaction that may contribute to the development of abnormal vascular tone.