The role of cyclic GMP in cells with the properties of smooth muscle cultured from the rat myometrium

Cells growing in culture with previously described properties of rat uterine smooth muscle accumulated 45 Ca 2+ from the medium. Ca 2+ uptake by these cells was stimulated by the addition to the medium of 8‐bromo‐cGMP but not by 8‐bromo‐cAMP. Ca 2+ uptake was also stimulated by carbachol and by the nitro‐vasodilator nitroprusside. Although cholinergic agonists have been shown previously to stimulate contraction but not cGMP synthesis in the rat myometrium, both carbachol and nitroprusside stimulated cGMP production by the cultured cells. These results suggested the cells had cholinergic receptor‐mediated functions that reflected some neurotransmitter‐sensitive properties of uterine smooth muscle in situ. When determined by a specific radioligand binding assay, subcellular fractions of the cultured cells bound muscarinic cholinergic agonists and antagonists with affinities expected of the muscarinic receptor. The cells were also sensitive to the β‐adrenergic catecholamine agonist isoproterenol, which stimulated cAMP production but not Ca 2+ uptake. Carbachol failed to inhibit isoproterenol‐dependent cAMP production, which is an important property of the cholinergic receptor in uterine smooth muscle in situ. These results suggest some but not all acetylcholine‐sensitive properties of uterine smooth muscle may be retained in cell culture.