Pressure changes and instantaneous frequency plot of an isolated guinea pig bladder induced by arecaidine. A. Pressure changes of an isolated guinea pig bladder induced by 1 μM arecaidine. The average frequency in the initial phase, defined as the first 2 minutes after arecaidine application, is labelled Fini. The steady state frequency (Fsteady) is defined as the average frequency over a 5 minutes period prior to the wash out. B. Instantaneous frequency plot of an isolated guinea pig bladder. The time of stimulation with 1 μM arecaidine is indicated with an arrow. The frequency of the autonomous contractions initially increases and then return back to a lower steady level after approximately 5 minutes.