Effects of the amphiphilic peptides mastoparan and adenoregulin on receptor binding, G proteins, phosphoinositide breakdown, cyclic AMP generation, and calcium influx

Abstract

1. The amphiphilic peptide mastoparan is known to affect phosphoinositide breakdown, calcium influx, and exocytosis of hormones and neurotransmitters and to stimulate the GTPase activity of guanine nucleotide-binding regulatory proteins. Another amphiphilic peptide, adenoregulin was recently identified based on stimulation of agonist binding to A₁-adenosine receptors. 2. A comparison of the effects of mastoparan and adenoregulin reveals that these peptides share many properties. Both stimulate binding of agonists to receptors and binding of GTPγS to G proteins in brain membranes. The enhanced guanyl nucleotide exchange may be responsible for the complete conversion of receptors to a high-affinity state, complexed with guanyl nucleotide-free G proteins. 3. Both peptides increase phosphoinositide breakdown in NIH 3T3 fibroblasts. Pertussis toxin partially inhibits the phosphoinositide breakdown elicited by mastoparan but has no effect on the response to adenoregulin.N-Ethylmaleimide inhibits the response to both peptides. 4. In permeabilized 3T3 cells, both adenoregulin and mastoparan inhibit GTPγS-stimulated phosphoinositide breakdown. Mastoparan slightly increases basal cyclic AMP levels in cultured cells, followed at higher concentrations by an inhibition, while adenoregulin has minimal effects. 5. Both peptides increase calcium influx in cultured cells and release of norepinephrine in pheochromocytoma PC12 cells. The calcium influx elicited by the peptides in 3T3 cells is not markedly altered byN-ethylmaleimide. 6. Multiple sites of action appear likely to underlie the effects of mastoparan/adenoregulin on receptors, G proteins, phospholipase C, and calcium.