Modulation of calcium sensitivity in guinea pig taenia coli: skinned fiber studies.

In summary then, skinned fiber experiments have provided evidence showing that the relationship between force development and free calcium ion concentration may be variable. The cyclic-nucleotides c-GMP (cf 38) and c-AMP in particular might be important in modulating calcium sensitivity of skinned fibers possibly via an alteration of myosin phosphorylation. Additionally, the coupling between myosin phosphorylation and the ATPase activity of actomyosin or tension generation may itself be modulated in actomyosin contractile systems. The recognition of the physiological relevance of these modulating mechanisms however must await experiments in which the relationship between force development, free calcium ion concentration and myosin phosphorylation is studied in intact fibers. With the advent of more sophisticated calcium measuring techniques, such information is now available.