Fig. 4. Surface plasmon resonance measurements – proportion of RyR1 binding to GST-FKBP12. RyR1 binding was normalised for GST-FKBP binding to the chip surface in each binding cycle. (A) Relationship between RyR1 bound (RU of RyR1 bound/RU of GST-FKBP12 bound to the chip) and RyR1 added. RyR1 was flowed over the chip in binding buffer containing EGTA (open circles), 1 mM Ca²⁺ (open squares), 1 µM Ca²⁺ (filled diamonds) and 1 µM Ca²⁺ + ATP (filled triangles). (B) The results for 1 µM ruthenium red (open circles) and 10 mM caffeine (filled diamonds). (C,D) Average of data from four experiments, with white and grey columns denoting agents that open or close the channel, respectively. C compares 1 µM Ca²⁺, 1 µM Ca²⁺ + ATP, and 1 mM Ca²⁺ with the value for 1 mM EGTA. D compares the binding with 10 mM caffeine with that for 1 µM ruthenium red. n = 4 ± s.e.m., *P<0.05, unpaired Student's t test.