The effect of NOC-5 on the release of Ca²⁺ through IP₃Rs. (A) Fluorescence image of part of an airway indicating the area (white circle) within an SMC exposed to light to uncage IP₃, the ROI (white square) used to determine the changes in [Ca²⁺]_i with respect to time and the row of pixels (dashed line) used for line scan analysis plotted in B. The position of both the ROI and the line scan were adjusted to track the same area inside the SMC during airway contraction. (B) Simultaneous changes in Ca²⁺ signaling (top traces and line scans) and contraction (bottom traces) triggered by uncaging IP₃ with UV flashes (arrows) in the absence or presence of 10 µM NOC-5 (top bar). The airway was allowed to relax completely between challenges with UV flashes to assure that the same area within the SMC was illuminated. In the absence of NOC-5, each UV flash triggered a transient increase in [Ca²⁺]_i (trace) that was initiated in the flash area and propagated along the SMC as a Ca²⁺ wave (white vertical line in line scan). The Ca²⁺ wave was accompanied by a transient airway contraction (bottom). Perfusion with NOC-5 (top bar) blocked the Ca²⁺ transient and the contraction triggered by releasing IP₃. Representative data from seven different slices from two mice are shown. (C) Ca²⁺ signaling in airway SMCs and airway contraction stimulated by 20 mM caffeine in the absence or presence of 10 µM NOC-5 (top bars). NOC-5 had no apparent effect on the Ca²⁺ signal and contraction induced by caffeine. Representative data from four different slices from two mice are shown. A movie showing the effect of NOC-5 on the Ca²⁺ waves triggered by uncaging IP₃ in an SMC is shown in Video 3.