Biochemical analysis of triggering signals induced by bridging of IgE receptors

Bridging of IgE receptors on rat mast cell plasma membranes induces phospholipid methylation and a monophasic increase in cyclic AMP. The stimulation of phospholipid methylation in the plasma membrane appears to be intrinsic to the processes leading to Ca²⁺ influx and histamine release. Evidence was obtained that IgE receptors are closely associated with methyltransferases and adenylate cyclase in the plasma membranes. The activation of one enzyme is regulated by the other. An increase in the cyclic AMP level before receptor bridging suppressed phospholipid methylation. On the other hand, inhibition of phospholipid methylation may affect the initial rise in cyclic AMP. Our experiments also indicated that bridging the receptor activates a membrane-associated proteolytic enzyme. Inasmuch as the inhibition of the enzyme activation results in the suppression of both phospholipid methylation and initial rise in cyclic AMP induced by receptor bridging, the proteolytic enzyme may be involved in the activation of methyltransferases and adenylate cyclase.