α_t -Adrenergic receptors (AR) play an important role in the regulation of physiological responses mediated by norepinephrine and epinephrine, particularly in the cardiovascular system. The three cloned oc,-AR subtypes (α_(1A) α_(1B) and α_(1D)) are G protein-coupled receptors that signal through the G_(q/11) signaling pathway, each showing distinct pharmacological properties and tissue distributions. However, due to the lack of highly subtype-selective drugs, the functional roles of individual subtypes are still not clear. Development of new subtype-specific drugs will greatly facilitate the identification of the functions of each subtype. Conopeptide TIA has been found to be a new α_(1B)-AR selective antagonist with different modes of inhibition at α_1-AR subtypes. In addition, recent studies using genetically engineered mice have shed some light on α_1AR functions in vivo, especially in the cardiovascular system and brain. Several proteins have been shown to interact directly with particular α_1-AR, and may be important in regulating receptor function. Receptor heterodimerization has been shown to be important for cell surface expression, signaling and internalization. These new observations are likely to help elucidate the functional roles of individual a,-AR subtypes. α_t-Adrenergic receptors (AR) play an important role in the regulation of physiological responses mediated by norepinephrine and epinephrine, particularly in the cardiovascular system. The three cloned oc, -AR subtypes (α_ (1A) α_ (1B) and α_ )) G protein-coupled receptors that signal through the G_ (q / 11) signaling pathway, each showing distinct pharmacological properties and tissue distributions. However, due to the lack of highly subtype-selective drugs, the functional roles of individual subtypes are still not clear. Development of new subtype-specific drugs will greatly facilitate the identification of the functions of each subtype. Conopeptide TIA has been found to be a new α - (1B) -AR selective antagonist with different modes of inhibition at α_1-AR subtypes In addition, recent studies using genetically engineered mice have shed some light on α_1AR functions in vivo, especially in the cardiovascular system and brain. Several proteins have been shown to interact directly with particular α_1-AR, and may be important in regulating receptor function. Receptor heterodimerization has been shown to be important for cell surface expression, signaling and internalization. These new observations are likely to help elucidate the functional roles of individual a, -AR subtypes .