Specific properties of smooth muscle cells from different layers of rabbit myometrium.

Myometrial cells were isolated from rabbit uterine horns previously stripped of endometrium and oriented to submit the inner circular (CIRC) or the outer longitudinal (LONG) layer to enzyme dispersal. Cells from both layers attached to the culture dishes within 72 h, reached confluency around day 7, and exhibited different morphological patterns. Indirect immunofluorescence with antidesmin antibody revealed that both preparations were at least 80% smooth muscle. Similarly, electron microscopy confirmed the presence of microfilaments in both cell types and revealed characteristic ultrastructural features of smooth muscle cells. Cultured cells from CIRC appeared larger on the phase-contrast microscope, with a mean apparent surface area of 0.105 mm2 for circular and 0.067 mm2 for longitudinal cells. Adenylate cyclase activity in general was higher in circular than in longitudinal cells (P less than or equal to 0.05), but a significant beta-adrenergic response to isoproterenol was observed only for longitudinal cells. This cell culture model is thus useful in defining the specific properties and functions of the different myometrial layers in the regulation of uterine contractility.