S-Nitrosylation-Mediated Reduction of Ca_V1.2 Surface Expression and Open Probability Underlies Attenuated...

L-type Ca_V1.2 calcium channel, the primary gateway for Ca²⁺ influx in smooth muscles, is widely regulated by multiple posttranslational modifications, such as protein kinase-mediated phosphorylation and nitric oxide-induced S-nitrosylation. However, the effect of S-nitrosylation on Ca_V1.2 channel function and its role in arterial contractility are not well understood.

Electrophysiological recordings, Ca²⁺ and confocal imaging, and biochemical assays were used to functionally characterize S-nitrosylated Ca_V1.2 channels in vitro, while pressure myography and tail-cuff blood pressure measurement were conducted to evaluate the physiological effects of Ca_V1.2 S-nitrosylation ex vivo and in vivo.

S-nitrosylation significantly reduced the Ca_V1.2 current density by promoting lysosomal degradation that leads to decreased levels of total and surface Ca_V1.2 channel proteins in a Ca_Vβ-independent manner and reducing the open probability of Ca_V1.2 channel. Mechanistically, the Cys1180 and Cys1280 residues within Ca_V1.2 channel have been determined as the molecular targets for S-nitrosylation as substitution of either Cys1180 or Cys1280 for serine resulted in substantial reduction of S-nitrosylation levels. Of note, Ca_V1.2 S-nitrosylation levels were significantly reduced in arteries isolated from both spontaneously hypertensive rats and patients with pulmonary hypertension. Moreover, mouse resistance arteries incubated with S-nitrosocysteine displayed much lower contractility and spontaneously hypertensive rats injected with S-nitrosocysteine also showed significantly reduced blood pressure, suggesting that reduced S-nitrosylation contributes to the upregulation of Ca_V1.2 channel activity in hypertensive arteries.

This study provides strong evidence that S-nitrosylation-mediated downregulation of Ca_V1.2 channels is via 2 distinctive mechanisms and the findings offer potential pathways for therapeutic inventions in hypertension.