Figure 5.

Stimulation of [³H]ryanodine binding to RyR1 by Intrepicalcin (A) Dose-dependent activation of Intrepicalcin on RyR1 between 1 pM and 1 μM (n=3). Heavy SR from rabbit skeletal muscle were incubated with 5 nM [³H]ryanodine in the absence (control) and the presence of indicated concentrations of Intrepicalcin. Binding conditions were specified in Methods. The K_d was determined with the formula B = (B_max)/[1 + (K_d/[Intrepicalcin])^nH), where B is specific binding of [³H]ryanodine, B_max is the maximum binding stimulated by Intrepicalcin, and nH is the Hill coefficient. (B) Ca²⁺ sensitivity of [³H]ryanodine binding affected by Intrepicalcin at 100 nM (n=3). The specific [³H]ryanodine binding was standardized with the value of the control at pCa5 as 100%.