Fig. 5

Effects of MgADP or Pi on Ca²⁺ sensitivity in rabbit psoas muscle fibers at SL 2.4 and 2.8 μm. a Comparison of force–pCa curves (top) and passive force (bottom) in the two different SL ranges [short (2.0 and 2.4 μm) and long (2.4 and 2.8 μm)] under the control condition without MgADP or Pi. Passive force was significantly (P < 0.05) greater at each point in the long SL range throughout the experiment [i.e., 2.0 μm (short) vs. 2.4 μm (long); 2.4 μm (short) vs. 2.8 μm (long)]. Black solid lines force–pCa curves in the short SL range (same as in Fig. 2). Black dashed lines force–pCa curves in the long SL range. Inset ΔpCa₅₀ in the short and long SL ranges. *P < 0.05; n = 6. b Effect of 3 mM MgADP on force–pCa curves (top) and passive force (bottom) in the long SL range. Black dashed lines (same as in a) –MgADP, red dashed lines +MgADP. Inset ΔpCa₅₀ in the absence and presence of MgADP. C control without MgADP. *P < 0.05; n = 6. c Effect of 20 mM Pi on force–pCa curves (top) and passive force (bottom) in the long SL range. Black dashed lines (same as in a, b) −Pi, blue dashed lines +Pi. Inset comparison of ΔpCa₅₀ in the absence and presence of Pi. *P < 0.05; n = 6. Passive force was not significantly altered by MgADP or Pi at either 2.4 or 2.8 μm (b, c)