Pharmacology and force development of single freshly isolated bovine carotid artery smooth muscle cells

Abstract

Most studies of mammalian vascular smooth muscle cell mechanics and pharmacology have relied upon data from intact tissue preparations. The purpose of this study was to determine how single mammalian vascular smooth muscle cell pharmacological sensitivity to histamine and force development compared to the intact tissue from which it was derived. Thus, techniques were developed for isolating large numbers (5 x 105 cells/ml) of cells from bovine carotid arteries. Single cells were spindle-shaped with dimensions of 117 ± 11 (SE) μm in length by 7 ± 1 (SE) μm in diameter (n = 27). The effect of histamine concentration on cell length was studied in suspensions of freshly isolated cells. Histamine concentration-response curves revealed that single smooth muscle cells shortened to histamine concentrations in a graded fashion, and that shortening was mediated through histamine H1 receptors. The threshold for 10% of maximum response occurred at 8.0 x 10-11 M histamine. This threshold was at least three orders of magnitude lower than the threshold for 10% of maximum tension in the intact tissue under isometric conditions. In addition to cellular pharmacology, mechanical studies were performed by tying a single cell to an ultrasensitive force transducer. Active stresses of 0.5 ± 0.1 x 105 N/m2 (n = 4) were measured in response to electrical stimulation for cells in low extracellular calcium (0.5 mM). These data suggest that histamine sensitivity and smooth muscle cell mechanics may best be determined in single cell studies that minimize diffusional barriers to agonist and avoid intercellular interactions that are present in the intact tissue.