Comparison of mouse skeletal SR K ⁺ single-channel events with those derived from HEK293 cell vesicles coexpressing TRIC-A or TRIC-B with RyR2 and with detergent-purified TRIC-B. (A) Typical SR K⁺ channel openings were observed after incorporating mouse skeletal muscle SR vesicles into bilayers in symmetrical 210 mM KPIPES, 2 µM free Ca²⁺ at the holding potential of +30 mV. The zero current level is indicated by “closed” and the fully open channel level by “open.” The orange and blue arrows indicate the characteristic rapidly gating subconductance states and slower gating full conductance openings. So that direct comparison can be made with the TRIC channel currents under identical recording conditions, B–D indicate the amplitude of a full SR K⁺ channel opening with a black arrow and the zero current level with “closed.” (B) Example of the currents observed after incorporating vesicles from HEK293 cells coexpressing RyR2+TRIC-A under the same experimental conditions as in A. (C) Example of the currents observed after incorporating vesicles from HEK293 cells coexpressing RyR2+TRIC-B under the same experimental conditions as in A. (D) Example of current fluctuations obtained after bilayer incorporation of CHAPS-purified TRIC-B channels expressed in yeast under the same experimental conditions as in A.