RLC phosphorylation influenced myocardial viscoelasticity under Ca²⁺-activated conditions at longer SLs. (A and B) Elastic moduli were plotted against frequency at 1.9-µm (A) and 2.2-µm (B) SLs for AP- and MLCK-treated skinned papillary muscle strips under maximally activated conditions (pCa 4.8) and submaximally activated conditions near half-maximal tension (pCa 5.5). (C and D) The associated viscous moduli were plotted against frequency at 1.9-µm (C) and 2.2-µm (D) SLs. Lines represent fits to Eq. 1 for the complex moduli versus frequency relationships. Because frequency varied at either pCa 4.8 or 5.5, moduli values differed between AP- and MLCK-treated conditions at 2.2 µm SL. *, P < 0.05; #, P < 0.1.