CHEMOTAXIS OF NEWT EOSINOPHILS - CALCIUM REGULATION OF CHEMOTACTIC RESPONSE

Local chemical events underlying chemotaxis were characterized in a ne w model cell, the newt eosinophil. These cells exhibit a chemotactic r esponse to a trypsin-sensitive component of newt serum. Ca2+ plays a r ole in this process, since treatments expected to diminish Ca2+ availa bility from the medium [ethylene glycol-bis(beta-aminoethyl ether)-N,N ,N',N'-tetraacetic acid, Co2+, and verapamil], to break down transmemb rane Ca2+ gradients (ionomycin), or to interfere with the function of intracellular Ca2+ stores (caffeine and neomycin) inhibited cell polar ization and movement. Using imaging techniques we found that cytosolic Ca2+ concentration ([Ca2+]i) increased in response to newt serum. Mig rating newt eosinophils exhibited a dynamic heterogeneous distribution of [Ca2+]i. [Ca2+]i was elevated in cells undergoing a change of dire ction relative to cells migrating persistently in one direction. Migra ting cells contained gradients of (Ca2+]i along their long axis, with the front of the cell having consistently lower [Ca2+]i than the rear. When cells were loaded with the cell-permeant form of fura 2, fura 2 acetoxymethyl ester, a caffeine-sensitive membrane-delimited region of elevated [Ca2+]i was seen associated with the microtubule organizing center. A model is proposed relating the distribution of [Ca2+]i and t he location of the external stimulus to the generation and interaction of substances within the cell that both simulate and inhibit increase s in [Ca2+]i.