Ca(V)3.2 Channels and the Induction of Negative Feedback in Cerebral Arterial Smooth Muscle

Ca V 1.2 (L‐type) along Ca V 3.1/Ca V 3.2 (T‐type) are the principal subtypes of voltage‐gated Ca 2+ channels (VGCC) expressed in cerebral arterial smooth muscle. While studies have long discerned the functional role of Ca V 1.2, the physiological significance of Ca V 3.x expression is uncertain. Recent immunohistochemical analysis noted that Ca V 3.2 localizes in close proximity to ryanodine receptors (RyR) on the sarcoplasmic reticulum. From these observations, we hypothesized that Ca V 3.2 triggers Ca 2+ ‐induced Ca 2+ release (RyR), activating large‐conductance Ca 2+ ‐activated K + channels (BK Ca ) to attenuate arterial constriction. Structural analysis involving immuno‐labeling approaches, electron microscopy, and 3D‐tomomography revealed a microdomain structure in cerebral arteries comprised of Ca V 3.2 and RyR. Using mathematical techniques, a microdomain model was subsequently developed and it revealed that Ca v 3.2 was capable of activating RyR and induce repetitive CICR‐like events. In keeping with these theoretical observations, perforated patch clamp electrophysiology revealed that Ni 2+ (50 μM, Ca v 3.2 inhibitor) attenuated the frequency and amplitude of BK Ca ‐mediated spontaneous transient outward currents (STOCs). Pressurized cerebral arteries were also shown to depolarized and constricted to micromolar Ni 2+ . The magnitude of these functional responses was comparable to paxilline, a BK Ca channel inhibitor. In summary, findings indicate for the first time that Ca V 3.2 channels are capable of driving a CICR‐like process that moderates arterial constriction through a feedback response involving BK Ca channels.