Figure 4. Fluorescence intensity due to excitation at 360 nm (F³⁶⁰) in two strips of canine tracheal smooth muscle during stimulation with 0.1 micro Meter acetylcholine. The rate of decline of F³⁶⁰produced by the addition of 0.5 mM Mn²+ was less in the strip exposed to ketamine (1 mM). F³⁶⁰was normalized to values before Mn sup 2+ addition and after lysis.