Fig. 7. Downregulation of InsP₃Rs and changes in Ca²⁺ puff characteristics in HeLa cells following prolonged agonist stimulation. (A) The effect of prolonged incubation with 1 mM histamine on the expression level of (i) IP₃R type 1 and (ii) IP₃R type 3 in HeLa cells. The immunoreactivity is expressed as a percentage of that in untreated cells. The data are expressed as mean±s.e.m. (n=3). (B) The functional loss of InsP₃Rs in cells incubated with 1 mM histamine for 6 hours assessed using ratiometric imaging of Fura2. The data are expressed as percentage (mean±s.e.m.) of the amplitude of the Ca²⁺ fluorescence signal in untreated cells. The number of experiments (n) is indicated in the bars. (C,D) The change in the Ca²⁺ puff characteristics following incubation of HeLa cells with 1 mM histamine for 4 hours.