Measurement of function in isolated single smooth muscle cells

Smooth muscle cells, isolated from the stomach of guinea pig, were anchored electrostatically to a poly-L-lysine-treated cover slip that formed the ceiling of a minichamber. The cells could be perfused at high flow rates for long periods without being dislodged. Contractile responses, measured by image-splitting micrometry, were obtained repeatedly and reproducibly at intervals of 5 s-5 min for up to 3 h. Peak response in single cells was attained in 1.5-2 min by comparison with peak response in suspensions of muscle cells (0.5 min). The delay was probably due to unstirred layers covering anchored single cells. Otherwise, the magnitude of response of single cells and their sensitivity to various agonists (C-terminal octapeptide of cholecystokinin, methionine-enkephalin, and acetylcholine), as expressed in the D50 values, were identical to those obtained from measurements on large populations (suspensions) of muscle cells. The identity of dose-response profiles of single cells and suspensions of cells, particularly the wide span of the dose-response curves and the low Hill coefficients (0.30-0.35), implied that receptor heterogeneity was an inherent property of each muscle cell rather than a reflection of differences between muscle cells. This simple, precise, and economical method offers notable advantages in studies of isolated smooth muscle cells.