The human neutrophil participates in the important reactions of chemotaxis and enzyme release. The plasma membrane performs both structural and regulatory roles in these reactions. Membrane bound PGE1 and beta adrenergic receptors (class 2 receptors) inhibit chemotaxis and enzyme release while FMLP and C5a (class 1 receptors) function as promoters. Both classes of receptors are modulators of cyclic nucleotides. Thus, class 1 receptors cause transient increases in cAMP and cGMP while class 2 receptors cause steady state increases in cAMP. Two aspects of these observations remain unclear: (a) What is the biochemical basis for receptor modulation of cyclic nucleotides? (b) In mechanistic terms what is effector role for cyclic nucleotides in control of chemotaxis and enzyme release? These closely linked questions are investigated as follows: (a) A structurally well defined hormonally sensitive plasma membrane has been prepared from human neutrophils, and major proteins and glycoproteins have been identified. (b) Enzymes of cyclic nucleotide metabolism (adenylate and guanulyate cyclases, phosphodiesterase will be identified and the major (non receptor) regulators (guanine nucleotides, free radicals, calmodulin) examined. (c) The presence of membrane bound receptors will be tested by direct binding studies. The regulation of receptors, interactions between class 1 and 2 receptors, and correlation of binding with cellular control will be probed. (d) Receptor linkages to the enzymes will then be tested in the membrane and whole cell. Receptor potency of enzyme activation will be correlated with receptor control of cellular function. In the light of these experiments, mechanisms of receptor modulation of cyclic nucleotides will be evaluated. The cellular significance of cyclic nucleotide modulation will be established by the identification of: (a) nucleotide sensitive kinases, (b) membrane bound kinase substrates, (c) consequences for cell function of persistent in vivo alteration of cyclase and diesterase systems. The results should provide detailed information into the biochemical basis and the significance of the modulation of cyclic nucleotides in the human neutrophil.
