Fig. 5. Downregulation of InsP₃Rs in SH-SY5Y cells. (A) The effect of prolonged incubation with 1 mM carbachol on the expression level of (i) InsP₃R type 1 and (ii) InsP₃R type 3 in SH-SY5Y cells. Typical examples of the immunoband at 261 kDa and 248 kDa for types 1 and 3 InsP₃Rs are shown above the histograms. The immunoreactivity is expressed as a percentage of that in untreated cells. The data are expressed as mean±s.e.m. (n=3). All data were significantly different from control (P<0.05). (B) The functional loss of InsP₃Rs in cells incubated with 1 mM carbachol for 6 hours. To provide a more reliable estimate of the global Ca²⁺ response, we used ratiometric imaging of Fura2 rather than single wavelength confocal recording. 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.