Alpha-2 adrenoceptors couple with G protein alpha-i subtype which decreases adenylyl cyclase activity, thus reducing cAMP intracellular levels resulting in smooth muscle contraction. There are three alpha-2 subtypes in humans; 2A (Kobilka BK et al, 1987), 2B (Weinshank RL et al, 1990) and 2C (Hirasawa A et al, 1993).
Kobilka, BK, Matsui, H, Kobilka, TS, Yang-Feng, TL, Francke, U, Caron, MG, Lefkowitz, RJ, Regan, JW
Hirasawa, A, Horie, K, Tanaka, T, Takagaki, K, Murai, M, Yano, J, Tsujimoto, G
Weinshank, RL, Zgombick, JM, Macchi, M, Adham, N, Lichtblau, H, Branchek, TA, Hartig, PR
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