K+-dependent development of window contraction. Isometric contractions induced by addition of 3.5 mM Ca2+ to 0Ca containing 10 up to 124 mM K+ (A). Absolute (B) and relative (50 mM K+ set to 100%, C) [K+]-force curves were determined at 200, 400 and 600 s (see dotted lines in A), were bell-shaped and could only be fitted up to 50 mM K+ (B, C). Results show mean ± s.e.m, n = 6. *, **, ***: P<0.05, 0.01, 0.001 versus 50 mM K+.