European Journal of Pharmacology - Molecular Pharmacology Section, 172 (1989) 1-7 1 Elsevier EJM 90001 Heterologous regulation of EGF receptor function in cultured aortic smooth muscle cells Jonathan Blay and Morley D. Hollenberg * Endocrine Research Group, Department of Pharmacology and Therapeutics, University of Calgary, Faculty of Medicine, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada Received 27 July 1988, revised MS received 12 October 1988, accepted 1 November1988 A10 cultured smooth muscle cells from rat embryonic thoracic aorta bound 125I-labelled epidermal growth factor (125I-EGF), and responded to EGF by an increase in DNA synthesis. Scatchard analysis of binding data obtained at 4°C showed curvilinearity consistent with there being two affinity classes of binding site. The amount of 125I-EGF that bound was decreased by treatment of the A10 cells at 37 o C with [ArgS]vasopressin or with 5-hydroxytryptamine (5-HT). Scatchard analysis of binding (at 4°C after pretreatment at 37 o C) revealed this effect to be due to a loss of the high-affinity component of a25I-EGF binding, with no change in total receptor number. The presence of vasopressin or 5-HT raised the concentration of EGF required for the stimulation of DNA synthesis. Cultured A10 aortic smooth muscle cells therefore have receptors for EGF that mediate an increase in cell proliferation. EGF receptor function is modified by vasopressin and 5-HT, probably as a consequence of their effects on EGF receptor affinity. Vascular smooth muscle; Epidermal growth factor receptors; Epidermal growth factor-urogastrone; Vasopressins; Serotonin 1. Introduction Although 25 years have passed since epidermal growth factor (EGF) was first discovered, we still do not know what physiological role(s) it may fulfil. In addition to being a mitogen, EGF can act as a growth inhibitor (Blay and Brown, 1986), as a promoter of cell migration (Blay and Brown, 1985a), and as a regulator of differentiated cell functions in various systems (see Carpenter, 1981). Recently, it has been observed that EGF may also have effects on smooth muscle contractility. EGF induces contraction in tissue strips from rat aorta (Berk et al., 1985), rat ileocolic artery (Muramatsu et al., 1985), rat uterus (Gardner et al., 1987), * To whom all correspondenceshould be addressed. guinea pig stomach (Muramatsu et al., 1988) and guinea pig trachea (Patel et al., 1988). In contrast, EGF inhibits the contraction induced by other stimuli in certain tissues, including dog mesenteric artery (Muramatsu et al., 1986) and dog coronary artery (Gan et al., 1987b). Such effects on smooth muscle appear also to take place in the intact animal. EGF produces vasodilatation in various vascular beds of the dog (Gan et al., 1987b), and recent evidence suggests that EGF may act as a vasoconstrictor in the rat pulmonary circulation (Rippetoe et al., 1988). In order to begin to define the pathway(s) of EGF action in smooth muscle cells, we have turned our attention to cultured cell systems. EGF has been shown to bind to specific receptors on cells cultured from both vascular (aortic) and visceral (uterine) smooth muscle (Bhargava et al., 1979). 0922-4106/89/$03.50 © 1989 Elsevier Science Pubfishers B.V. (Biomedical Division)