Intracellular calcium changes induced by the endozepine triakontatetraneuropeptide in human polymorphonuclear leukocytes: role of protein kinase C and effect of calcium channel blockers

BACKGROUND: The endozepine triakontatetraneuropeptide (TTN) induces intracellular calcium ([Ca(++)](i)) changes followed by activation in human polymorphonuclear leukocytes (PMNs). The present study was undertaken to investigate the role of protein kinase (PK) C in the modulation of the response to TTN by human PMNs, and to examine the pharmacology of TTN-induced Ca(++ )entry through the plasma membrane of these cells. RESULTS: The PKC activator 12-O-tetradecanoylphorbol-13-acetate (PMA) concentration-dependently inhibited TTN-induced [Ca(++)](i )rise, and this effect was reverted by the PKC inhibitors rottlerin (partially) and Ro 32-0432 (completely). PMA also inhibited TTN-induced IL-8 mRNA expression. In the absence of PMA, however, rottlerin (but not Ro 32-0432) per se partially inhibited TTN-induced [Ca(++)](i )rise. The response of [Ca(++)](i )to TTN was also sensitive to mibefradil and flunarizine (T-type Ca(++)-channel blockers), but not to nifedipine, verapamil (L-type) or ω-conotoxin GVIA (N-type). In agreement with this observation, PCR analysis showed the expression in human PMNs of the mRNA for all the α1 subunits of T-type Ca(++ )channels (namely, α1G, α1H, and α1I). CONCLUSIONS: In human PMNs TTN activates PKC-modulated pathways leading to Ca(++ )entry possibly through T-type Ca(++ )channels.