Ca2+from intracellular Ca2+stores does not contribute to K+contractions. Effects of 15 μM ryanodine on baseline isometric tension (A), and on force evoked by 20 mM caffeine (B) or 50 mM K+ (C). Results show mean ± s.e.m, n = 4. *, ***: P<0.05, 0.001, control versus ryanodine. Effects of 50 μM 2-APB on contraction induced by 2 μM PE in 0Ca solution (D) or contraction induced by 50 mM K+ (E). Results show mean ± s.e.m, n = 4. **, ***: P<0.01, 0.001, control versus 2-APB. (F) Dose–response curve for inhibition by nifedipine of the contractions evoked by 50 mM K+ (n = 4).