HCO3- ions modify the role of PKC isoforms in the modulation of rat mast cell functions

PKC and the intracellular calcium signal are two well-known intracellular s ignaling pathways implicated in the induction of mast cell exocytosis. Both signals are modified by the presence or absence of HCO3- ions in the exter nal medium. In this work, we studied the regulation of the exocytotic proce ss by PKC isozymes and its relationship with HCO3- ions and PKC modulation of the calcium entry. The calcium entry, induced by thapsigargin and furthe r addition of calcium, was inhibited by PMA, a PKC activator, and enhanced by 500 nM GF109203X, which inhibits Ca2+-independent PKC isoforms. PMA inhi bition of the Ca2+ entry was reverted by 500 and 50 nM GF109203X, which inh ibit Ca2+-independent and Ca2+-dependent isoforms, respectively, and Go6976 , a specific inhibitor of Ca2+-dependent PKCs. Thus. activation of Ca2+-dep endent and Ca2+-independent PKC isoforms inhibit Ca2+ entry in rat mast cel ls, either in a HCO3--buffered or a HCO3--free medium. PMA, GF109203X, Go69 76 and rottlerin, a specific inhibitor of PKC delta, were also used to stud y the role of PKC isoforms in the regulation of exocytosis induced by thaps igargin. ionophore A23187 and PMA. The results demonstrate that Ca2+-depend ent PKC isoforms inhibit exocytosis in a HCO3--dependent way. Moreover, Ca2 +-independent PKC delta was the main isoform implicated in promotion of Ca2 +-dependent roast cell exocytosis in the presence or absence of HCO3. The r ole of PKC isoforms in the regulation of mast cell exocytosis depends on th e stimulus and on the presence or absence of HCO3- ions in the medium, but it is independent of PKC modulation of the Ca2+ entry. (C) 2001 Elsevier Sc ience Inc. All rights reserved.