Fig. 4. Caffeine response of RyR1- and RyR3-expressing cells. RyR1- or RyR3-expressing HEK 293 cells were loaded with 5 µM Fura 2-AM for 30 minutes and analyzed for caffeine-induced Ca²⁺ release at excitation wavelength of 340 and 380 nM. Release was normalized on the maximum Ca²⁺ release at 5 mM caffeine. Bars indicate the mean±s.e.m. of the percentage of Ca²⁺-release increments induced by different caffeine concentrations.