Evidence for myosin-linked regulation in guinea pig taenia coli muscle

The ATPase activity of actomyosin prepared from taenia coli muscle of guinea pig was found to increase upon adding rabbit skeletal heavy meromyosin (HMM) in the absence of Ca²⁺. SDS-gel electrophoresis of muscle homogenates did not reveal the presence of troponin. Ca²⁺-regulation in taenia coli muscle thus appears to be myosin-linked. The glycerinated muscles which did not develop any tension in the presence of EGTA contracted after irrigation with rabbit skeletal myosin. Skeletal HMM could also cause tension generation in strips of glycerinated taenia coli in the presence of EGTA. The tension developed by the muscles in the presence of Ca²⁺ was increased if HMM was added. The HMM-induced tension was associated with a marked increase in ATPase activity both in the presence and in the absence of Ca²⁺. No HMM-associated tension could be detected when inactivated HMM was employed or when MgATP was substituted with Mg-pyrophosphate or Mg-AMP-PNP. The mechanical effect of HMM probably results from a mechanochemical interaction between the added HMM and muscle actin.