Figure 8. Calcium²+-tension relation in beta-escin-permeabilized strips. (A) A 143 mM Potassium sup +-induced contraction in an intact strip followed by Calcium²+-activated contraction in the same strip after beta-escin permeabilization. (B) The Calcium²+-tension relation in beta-escin-permeabilized strips. The EC⁵⁰value derived from the least-squares fit by the logistic equation [45] was 2.02 micro Meter. The magnitude of Calcium²+-activated contractions was normalized to maximum (100 micro Meter) Calcium²+-activated contraction, and all values represent mean plus/minus SEM (n = 5, five animals).