Time-Dependent Decrease in Ca2+-Sensitivity in “Phasic Smooth Muscle”
Recent studies using the Ca2+-indicators, aequorin and fura-2, support the concept that increased intracellular Ca2+ ([Ca2+ ]i) leads to force development in smooth muscle (for reviews, see Karaki, 1989; Somlyo and Himpens, 1989). For example, in guinea-pig taenia caecum a close correlation exists between [Ca2+]i and muscle tension (Ozaki et al., 1988; Mitsui and Karaki, 1990). However, in some smooth muscles, the relationship between [Ca2+]i and force development appears to depend upon the method of stimulation. For a given increase in [Ca2+]i, agonists such as norepinephrine, histamine, prostaglandins, and endothelin in vascular smooth muscle (Morgan and Morgan, 1984; DeFeo and Morgan, 1985; Sato et al., 1988; Sakata et al., 1989; Mori et al., 1990; Ozaki et al., 1990a), and carbachol in trachea (Gerthoffer et al., 1990; Ozaki et al., 1990b) induce greater contractions than simple depolarization with elevated external K+. These findings suggest that the Ca2+-sensitivity of the contractile elements may be increased by certain agonists. Although the mechanism of Ca2+-sensitization has not been clarified, the agonist-induced activation of protein kinase C and subsequent phosphorylation of specific protein(s) may be involved.
KeywordsHistamine Prostaglandin Norepinephrine Acetylcholine Photolysis
Unable to display preview. Download preview PDF.
- DeFeo, T. T. and Morgan, K. G., 1985, Calcium-force relationship as detected by aequorin in two different vascular smooth muscle of the ferret, J. Physiol., 369: 269.Google Scholar
- Gerthoffer, W. T., Murphey, K. A., and Gunst, S. J., 1989, Aequorin luminescence, myosin phosphorylation, and active stress in tracheal smooth muscle, Am. J. Physiol., 257: C1062.Google Scholar
- Golenhofen, K., 1976, Theory of P and T systems for calcium activation in smooth muscle, in: “Physiology of Smooth Muscle”, E. Bülbring and M. F. Shuba, eds., Raven Press, New York, p. 197.Google Scholar
- Golenhofen, K., 1981, Differentiation of calcium activation processes in smooth muscle using selective antagonists, in: “Smooth Muscle: An Assessment of Current Knowledge”, E. Bülbring, A. F. Brading, A. W. Jones, and T. Tomita, eds., University of Texas Press, Austin, p. 157.Google Scholar
- Hartshorne D. J., 1987, Biochemistry of the contractile process in smooth muscle, in: “Physiology of Gastrointestinal Tract”, L. R. Johnson, ed., Raven Press, New York, p. 423.Google Scholar
- Ishihara, H., Martin, B. L., Brautigan, D. L., Karaki, H., Ozaki, H., Kato, Y., Fusetani, N., Watabe, S., Hashimoto, K., Uemura, D., and Hartshorne, D. J., 1989, Calyculin A and okadaic acid: Inhibitors of protein phosphatase activity, Biochem. Biophys. Res. Commun., 159: 871.PubMedCrossRefGoogle Scholar
- Morgan, J. P. and Morgan, K. G., 1984, Stimulus-specific patterns of intracellular calcium levels in smooth muscle of ferret portal vein,J. Physiol., 351: 312.Google Scholar
- Sanders, K. M. and Publicover, N. G., 1989, Electrophysiology of the gastric musculature, in: “Handbook of Physiology, The Gastrointestinal System,” Vol I., S. G. Schultz and J. D. Wood., eds., The American Physiological Society, Bethesda, p. 187.Google Scholar
- Szurszewski, J. H., 1987, Electrical basis for gastrointestinal motility, in: “Physiology of Gastrointestinal Tract”, L. R., Johnson, ed., Raven Press, New York, p. 383.Google Scholar