Some Receptors May Inhibit Arachidonate Mobilization

By analogy with other transmembrane signaling systems—the cyclic AMP pathway for instance—one would expect the arachidonic acid cascade to be regulated both positively, as we have summarized above, and negatively. While evidence for an inhibitory control has been obtained, it is admittedly still very incomplete. In fact, to the best of my knowledge, only two examples of such control have been reported. 

Non-hydrolyzable GTP analogs (e.g., GTP-y-S) have played a very important role in determining the role of G proteins in transmembrane transduction. As a rule, their ability to produce a certain 

It appears from these results that certain transmembrane receptors may have the potential to be negatively coupled to the arachidonate cascade, at least under the artificial conditions of an heterologous expression system. Whether analogous responses may occur with receptors constitutively expressed in cells and tissues, remains a matter of conjecture. 

A THIRD GROUP OF RECEPTORS FACILITATE ARACHIDONATE MOBILIZATION, BUT DO NOT STIMULATE IT DIRECTLY 

Several neurotransmitter receptors share the ability to decrease adenylate cyclase activity in cells, through the intermediate of an Oi transducing G protein. When transfected in competent mammalian cells (e.g., CHO cells), receptors of this group produce, in addition to this classical effect on cyclic AMP accumulation, what 

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