Classification adenylate cyclase

Figure 4. Representation of the classification of the dopamine receptor based on its coupling with adenylate cyclase activity. DA+ receptors (left) are coupled to adenylate cyclase through the Ns GTP-binding protein (91) with secondary activation of adenylate cyclase. DA. receptors (middle) are coupled through the Ni GTP-binding protein, thus resulting in inhibition of cyclic AMP formation. DA0 receptors (right) are those uncoupled to cyclic AMP formation, the example being possibly some autoreceptors on nigrostriatal dopaminergic neurons.

The DA, and DA classification differs from other classifications basedion anatomical locations (presynaptic/postsynaptic) or response (increase in adenylate cyclase/no change in adenylate cyclase excitation/contraction). The subdivision of receptors described in this paper also differs from subdivisions based on the use of binding assays (2). 

The classification of dopamine receptors. Although Kebabian and Caine Q) performed an excellent service to the scientific community in proposing the D-l and D-2 receptor hypothesis, this remains to be proven by isolating and characterizing these receptors. These have been excellently reviewed by Cronin (2). Indeed the statement that the "D" receptors of the anterior pituitary are independent of adenylate cyclase is incorrect. We (3) and others (4, ) have shown a consistant and specific inhibitory relationship of the anterior pituitary dopamine receptor and adenylate cyclase. 

Kebabian and Caine have lately organized the available evidence into a coherent argument for classification of DA receptors as D-1 or D-2, according to whether or not they are linked to adenylate cyclase. Various criteria for this classification are listed in Table 1. 

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