BK_Ca channel subunits are located in close spatial proximity to IP₃R1 in cerebral artery smooth muscle cells. (A) Immuno-FRET data illustrating close spatial proximity of IP₃R1 to BK_Ca channel α subunits. Cy2- and Cy3-labeled secondary antibodies bound to IP₃R1 and BK_Ca channels generate N-FRET. In contrast, secondary antibodies bound to IP₃R1 and TRPM4 do not generate significant N-FRET. Bars, 10 µm. (B) Monoclonal IP₃R1 antibody coimmunoprecipitates IP₃R1 (∼270 kD), BK_Ca channel α (∼125 kD), and β1 (∼36 kD) subunits from cerebral arteries. Lysate supernatant was used as the input (+ve) control. Beads that have no antibody-binding capacity were used in the negative (−ve) coIP control.