Ultra-potent synthetic opioids such as fentanyl drive the majority of opioid-related deadly overdoses. Besides targeting neurons, fentanyl also exerts cerebrovascular effects. Epidemiological reports highlight variable actions of fentanyl on cerebral artery diameter and brain perfusion. However, the molecular targets of fentanyl in the vasculature remain unknown. While cerebral artery diameter is regulated by multiple factors, it is primarily determined by the activity of ion channels localized in the arterial myocyte plasmalemma. In particular, calcium-/voltage-gated potassium channels of large conductance (BKs) generate K + -currents that repolarize the myocyte plasmalemma and facilitate vasodilation. Cerebrovascular BKs are heterooligomers that include accessory β1 subunits ( KCNMB1 ). Computational docking of fentanyl on rat cerebrovascular BK β1 created by AlphaFold predicts hydrogen bonding between fentanyl and Glu13. Using high-throughput electrophysiology on CHO cells expressing BKs, we observed a concentration-dependent increase in whole-cell BK-mediated current amplitude by fentanyl (0.0001–10 microM) when β1 was co-expressed with BK-forming cbv1 subunits (cloned from rat cerebral artery myocytes). Recordings at Vhold = −80 mV, Vstep = +80 mV, Ca 2+ free = 3 microM rendered EC 50 = 15 nM and EC max = 200 nM for fentanyl action. Fentanyl failed to activate BKs in the absence of β1 subunits. To investigate the impact of β1-fentanyl interaction on organ function, middle cerebral arteries from adult C57BL/6J mice and Kcnmb1 -/- littermates were pressurized ex vivo (60 mmHg). In C57BL/6J arteries of males and females, fentanyl did not produce an effect on diameter. Arteries from Kcnmb1 -/- mice of both sexes constricted with increasing fentanyl concentrations. Thus, BK β1 subunits protect cerebral arteries from fentanyl-induced constriction. Whether the latter is direct (e.g., through fentanyl-β1 interaction) or involves opioid receptor signaling remains to be determined. In summary, fentanyl activates cerebrovascular BK channels via their β1 subunits. The latter represents a new target of fentanyl within the cerebral circulation.
Nooh et al. (Sun,) studied this question.