[Isolation, configuration and contractile responses of single smooth muscle cells]

In studies on the intrinsic contraction mechanisms of smooth muscle, various factors such as cell-to-cell interaction, penetration of chemicals to the trigger regions, or extracellular spaces in the tissue may influence the results. The use of single smooth muscle cells in such investigations may help to eliminate these factors. Single smooth muscle cells can be isolated from guinea pig taenia coli by digesting the minced tissue with a combination of collagenase and soybean trypsin inhibitor. The cells are spindle shaped, 100-200 microns in length and 10 microns in diameter. Three kinds of techniques for determination of contractile responses of single smooth muscle cells have been established: 1) fixation method, 2) perfusion method, and 3) capillary adhesion method. Using these techniques, the cells appeared to be contracted in a dose-dependent manner (graded response), while another mode of the contractile response, the "all-or-none response", has also been proposed. Scanning and transmission electron micrographs of the single cells revealed several evaginations of various sizes and shapes on the surface and electron dense bodies at the neck of the evaginations. ED50 obtained with the single cells, prepared from taenia coli of guinea pigs with collagenase in the presence of trypsin inhibitor was similar to that obtained with the intact tissue. Digestion of the tissue with highly purified collagenase and papain yields a large number of single cells with higher sensitivity to agonists. Characteristics of cells isolated from ileal longitudinal muscle of guinea pig are similar to those of cells isolated from taenia coli. The magnitude of contraction and sensitivity to acetylcholine were different in each cell. Incubation of isolated tissues with various concentrations of agonists followed by measurement of cell length in the tissue showed that the heterogeneous responses of the cells were intrinsic characteristics of smooth muscle cells and not due to damage incurred during the isolation procedure. Since isolated smooth muscle cells possess contractility, these might preserve the characteristics of smooth muscle, so they can be used for smooth muscle research. It must be considered, however, that each cell in the smooth muscle tissue has different contractility.