EFFECT OF SUBSTANCE-P AND ITS PRECURSOR ALPHA-PROTACHYKININ ON INTRACELLULAR FREE CALCIUM-CONCENTRATION IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES

The increase in intracellular free calcium concentration is an importa nt step in signal transduction leading to phagocyte activation. The un decapeptide substance P can influence various functions of human polym orphonuclear leukocytes, including chemotaxis, phagocytosis: and respi ratory burst. In this study we investigated the ability of low-concent ration (that can occur in vivo) substance P (10(-7) M) and its precurs or alpha-protachykinin (3 x 10(-7) M) to increase the intracellular fr ee calcium concentration in human polymorphonuclear leukocytes. Cells isolated from ten healthy donors were incubated with substance P or al pha-protachykinin in 1 mM calcium medium for 5 min and the intracellul ar free calcium concentration was monitored using the fluorescent calc ium indicator Fura-2am. Polymorphonuclear leukocytes from 40% of donor s responded to both agonists. The substance P- and alpha-protachykinin -induced increase in intracellular free calcium concentration was 59 /- 13 nM and 58 +/- 12 nM and the extracellular calcium influx contrib uted to 87 +/- 8 % and 54 +/- 8% of the calcium response, respectively . alpha-Protachykinin released almost all the calcium from intracellul ar stores, while substance P mobilized only 24 +/- 5% of this calcium pool. Finally, cells that responede to a single challenge with substan ce P and alpha-protachykinin were able to increase their intracellular free calcium concentration in response to each of three consecutive s timulations with these agonists. This may be an additional mechanism b y which substance P and its precursor modify the function of human pol ymorphonuclear leukocytes.