Angiotensin Induction of Active Responses in Cultured Reaggregates of Rat Aortic Smooth Muscle Cells

Abstract

Electrical activity was studied in cultured reaggregates of vascular smooth muscle cells prepared from the aortas of normotensive (WKY) and spontaneously hypertensive (SHR) rats. There were no significant differences between the resting membrane potentials of WKY (–44.7 ± 0.5 mV) and SHR (–45.6 ± 0.5 mV) reaggregates. Electrical field stimulation elicited active responses that consisted of two components: an initial spike component (amplitude, 30–40 mV; +V_max 1–3 V/s) and a plateau component (amplitude, 10–30 mV; duration 3–5 s; +V_max, 0.1–0.3 V/s). Often the spike component was absent. Both components of the response were abolished by verapamil, Mn⁺⁺, and Na⁺-free solutions indicating that Na⁺ and Ca⁺⁺ currents may be associated with them. Addition of 10 m M TEA increased the duration of the response, and addition of 0.5 m M BaCl₂ to the TEA solution increased the duration even further. The spike component always occurred in the presence of TEA and Ba⁺⁺. No differences were observed between responses in WKY and SHR reaggregates. A bolus of angiotensin II (All) (bolus concentration of 1 µM) elicited a transient depolarization. In some cells an active membrane response was triggered by the depolarization and sometimes included the spike component. Replacing all the Na⁺ in the solution with either Tris or choline resulted in loss of the response to All, and in some cells a hyperpolarization was actually seen on addition of the AH. The response to All was insensitive to verapamil (up to 10^–5 M), but was blocked by 1 m M MnCl₂. Reaggregates from both WKY and SHR animals gave similar responses to AIL The data indicates that cultured reaggregates of vascular smooth muscle are electrically excitable and are sensitive to angiotensin. Therefore functional angiotensin receptors must be present in the cultured cells.