Some properties of chemically skinned single smooth muscle cells.

Properties of isolated single smooth muscle cells in which the surface membrane has been made highly permeable by saponin treatment are described. The single cells were isolated from guinea pig taenia caeci by digestion with collagenase and skinned in a relaxing solution by treatment with 7 micrograms/ml saponin for 10 min. The skinned single cells showed Ca2+-regulated shortening in the presence of Mg-ATP, and the maximum degree of shortening was larger than that of the potassium-induced shortening observed in the intact isolated single cells. The half maximum shortening of the skinned single cells occurred at about 5 x 10(-8) Ca2+. The skinned single cells showed a significantly higher Ca2+-sensitivity than the skinned fiber bundles. The shortening-pCa curve for the skinned single cells was unchanged by alteration of pH and ionic strength, but it was shifted to the left by increasing MgATP concentration or to the right by increasing free Mg2+ concentration. The skinned single cells retained their internal Ca2+ storage site function. Caffeine induced shortening in the skinned single cells preloaded with Ca2+, and this shortening was suppressed by procaine. The release of Ca2+ from the storage site could be produced and facilitated by Ca2+ itself when the skinned single cells were exposed to Ca2+ with a concentration of about 2 x 10(-8) M and this release was suppressed by procaine. These results suggest that the Ca2+-induced Ca2+ release mechanism may play a role in the regulation of the stored Ca2+ in this cell.