Inhibition of interleukin-8-activated human neutrophil chemotaxis by thapsigargin in a calcium- and cyclic AMP-dependent way

Chemotactic migration of human neutrophils, induced by interleukin-8 (IL-8) or other activators, was inhibited by thapsigargin in the high nanomolar r ange. The degree of inhibition depended on the type of activator. Other inh ibitors of Ca2+-ATPases associated with intracellular calcium stores, such as cyclopiazonic acid and 2,5-di-(tert-butyl)-1,4-benzohydroquinone, equall y inhibited IL-8-activated migration. Inhibition of migration by thapsigarg in and the other ATPase inhibitors occurred only in the presence of extrace llular Ca2+; migration was not inhibited in the presence of EGTA. La3+ reve rsed thapsigargin-induced inhibition to a large degree; other calcium chann el blockers gave a partial reversal (econazole, verapamil, and SK&F 96365) or had no effect (gadolinium chloride and Ni2+). Using electroporated cells and Ca buffers, it was shown that inhibition started at about 0.2 mu M and was complete at a cytosolic Ca concentration of about 2 mu M. it appears t hat under certain conditions the thapsigargin-induced influx of extracellul ar calcium, causing relatively high local calcium concentrations, initiates or permits a process which may be detrimental to chemotactic migration. Cy clic AMP (cAMP; adenosine 3',5'-cyclic monophosphate) is probably involved in this process, because thapsigargin increased the cAMP level and cAMP inh ibited IL-8-activated migration in a calcium-dependent way. The hypothesis that cAMP is involved in the effect of thapsigargin on migration is support ed by the finding that very low concentrations of thapsigargin stimulate ne utrophil migration in the absence of other chemoattractants. The results su ggest that thapsigargin causes a (compartmentalized) increase in cAMP, whic h results in a calcium-dependent modulation of migration. BIOCHEM PHARMACOL 59;4:369-375, 2000. (C) 2000 Elsevier Science Inc.