PHOSPHATIDIC-ACID INDUCES THE RELEASE OF BETA-GLUCURONIDASE BUT NOT LACTOFERRIN FROM ELECTROPERMEABILIZED HUMAN NEUTROPHILS

We studied the degranulation reaction of electropermeabilized human ne utrophils induced by 1,2-didecanoyl-3-sn-phosphatidic acid (PA(10)). P A(10) dose-dependently induced the release of beta-glucuronidase, an e nzyme of azurophil granules, but did not induce the release of lactofe rrin, a protein of specific granules. The enzyme release by PA(10) abs olutely required Ca2+, ATP, and Mg2+ and the concentrations for the ha lf-maximal response were 2.5 mu M, 60 mu M, and 0.25 mM, respectively. Although Ca2+ alone at concentrations higher than 10 mu M induced the release of both beta-glucuronidase and lactoferrin, the extents of th e release were far less than that of the beta-glucuronidase release by PA(10). Phorbol myristate acetate (PMA) and 1-oleoyl-2-acetyl-sn-glyc erol induced the release of lactoferrin alone at concentrations of Ca2 + below 0.5 mu M while they induced the release of both beta-glucuroni dase and lactoferrin at higher Ca2+ concentrations, indicating that th e degranulation induced by PA(10) is not mediated by diacylglycerol wh ich might be formed from PA. The degranulation reactions induced by PA (10) and PMA were dose-dependently inhibited by staurosporine and calp hostin C, protein kinase C inhibitors, although no direct activation o f protein kinase C by PA(10), was observed. The extent of the beta-glu curonidase release by PA(10) was not enhanced by the addition of PMA. Propranolol, which inhibits protein kinase C as well as phosphatidic a cid phosphohydrolase, strongly inhibited the degranulation reactions i nduced by PA(10) and PMA. Ethanol, a metabolic modulator of phospholip ase D, and cyclic AMP did not affect the degranulation reactions by PM A and PA(10). These observations suggest that selective enzyme release from azurophil granules of the permeabilized neutrophils might be ind uced through the activation of protein kinase C or some other protein kinase sensitive to the protein kinase C inhibitors and that phospholi pase D may not be involved in the PMA-induced release.