Caveolae Link Ca_V3.2 Channels to BK_Ca-Mediated Feedback in Vascular Smooth Muscle

Objective- This study examined whether caveolae position Ca_V3.2 (T-type Ca2+ channel encoded by the α-3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca²⁺ influx to trigger Ca²⁺ sparks and large-conductance Ca²⁺-activated K⁺ channel feedback. Approach and Results- Using smooth muscle cells from mouse mesenteric arteries, the proximity ligation assay confirmed that Ca_V3.2 reside within 40 nm of caveolin 1, a key caveolae protein. Methyl-β-cyclodextrin, a cholesterol depleting agent that disrupts caveolae, suppressed Ca_V3.2 activity along with large-conductance Ca²⁺-activated K⁺-mediated spontaneous transient outward currents in cells from C57BL/6 but not Ca_V3.2^-/- mice. Genetic deletion of caveolin 1, a perturbation that prevents caveolae formation, also impaired spontaneous transient outward current production but did so without impairing Ca²⁺ channel activity, including Ca_V3.2. These observations indicate a mistargeting of Ca_V3.2 in caveolin 1^-/- mice, a view supported by a loss of Ni²⁺-sensitive Ca²⁺ spark generation and colocalization signal (Ca_V3.2-RyR) from the proximity ligation assay. Vasomotor and membrane potential measurements confirmed that cellular disruption of the Ca_V3.2-RyR axis functionally impaired the ability of large-conductance Ca²⁺-activated K⁺ to set tone in pressurized caveolin 1^-/- arteries. Conclusions- Caveolae play a critical role in protein targeting and preserving the close structural relationship between Ca_V3.2 and RyR needed to drive negative feedback control in resistance arteries.