Low Ca2+ impedes cross-bridge detachment in chemically skinned Taenia coli.
Muscle force is generated by cycling cross-bridges between actin and myosin filaments. In smooth muscle, cyclic attachment and detachment of cross-bridges is thought to be induced by a Ca2+- and calmodulin-dependent myosin light chain kinase which phosphorylates myosin. The relaxation that occurs after Ca2+ removal is usually ascribed to dephosphorylation of myosin by a phosphatase as non-phosphorylated myosin is unable to form force-generating criss-bridges. Recently, Dillon et al. claimed, however, that dephosphorylation of attached cross-bridges may impede cross-bridge detachment, thus forming so-called 'latch bridges'. Here we present evidence that after a Ca2+- and calmodulin-induced contraction of chemically skinned guinea pig Taenia coli, the rapid removal of Ca2+ impedes the detachment of the myosin cross-bridges from the actin filament; force can then be maintained without energy consumption. The extremely slowly detaching cross-bridges which maintain the force after Ca2+ removal may indeed correspond to the 'latch bridges' mentioned above.
D000199:Actins / Q000502:physiology; D000205:Actomyosin / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000502:physiology*; D006168:Guinea Pigs; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000502:physiology*; D009218:Myosins / Q000502:physiology*
D000199:Actins; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D009218:Myosins; D002118:Calcium