The non-tumour promoting irritant, resiniferatoxin, was capable of activating the NADPH-oxidase respiratory burst of starch-elicited, but not resident mouse peritoneal macrophages in vitro. Unlike TPA, the response was synergised by incubation with zymosan. The Rx-stimulated NADPH-oxidase activity in a cell-free assay was selectively enhanced in the presence of exogenous Rx-kinase rather than PKC and in the absence of Ca2+. Since resiniferatoxin is a poor activator of PKC, it is probable that the Ca2+-independent Rx-kinase plays a role in activation of the macrophage respiratory burst following stimulation by zymosan.
