α1_C S1928 Phosphorylation of Ca_V1.2 Channel Controls Vascular Reactivity and Blood Pressure

Increased vascular Ca_V1.2 channel function causes enhanced arterial tone during hypertension. This is mediated by elevations in angiotensin II/protein kinase C signaling. Yet, the mechanisms underlying these changes are unclear. We hypothesize that α1_C phosphorylation at serine 1928 (S1928) is a key event mediating increased Ca_V1.2 channel function and vascular reactivity during angiotensin II signaling and hypertension.

The hypothesis was examined in freshly isolated mesenteric arteries and arterial myocytes from control and angiotensin II-infused mice. Specific techniques include superresolution imaging, proximity ligation assay, patch-clamp electrophysiology, Ca²⁺ imaging, pressure myography, laser speckle imaging, and blood pressure telemetry. Hierarchical "nested" and appropriate parametric or nonparametric t test and ANOVAs were used to assess statistical differences. We found that angiotensin II redistributed the Ca_V1.2 pore-forming α1_C subunit into larger clusters. This was correlated with elevated Ca_V1.2 channel activity and cooperativity, global intracellular Ca²⁺ and contraction of arterial myocytes, enhanced myogenic tone, and altered blood flow in wild-type mice. These angiotensin II-induced changes were prevented/ameliorated in cells/arteries from S1928 mutated to alanine knockin mice, which contain a negative modulation of the α1_C S1928 phosphorylation site. In angiotensin II-induced hypertension, increased α1_C clustering, Ca_V1.2 activity and cooperativity, myogenic tone, and blood pressure in wild-type cells/tissue/mice were averted/reduced in S1928 mutated to alanine samples.

Results suggest an essential role for α1_C S1928 phosphorylation in regulating channel distribution, activity and gating modality, and vascular function during angiotensin II signaling and hypertension. Phosphorylation of this single vascular α1_C amino acid could be a risk factor for hypertension that may be targeted for therapeutic intervention.