CHANGES IN CYTOSOLIC CALCIUM CONCENTRATIONS AND CELL MORPHOLOGY IN SINGLE PLATELETS ADHERED TO FIBRINOGEN-COATED SURFACE UNDER FLOW

Changes in intracellular calcium concentration [Ca2+]i of fura-2-loade d human platelet during its adhesion to a fibrinogen-coated surface we re studied, using a flow chamber mounted on an epifluorescence microsc ope equipped with digital-ratio imaging. Adherent platelets were indiv idually mapped under a scanning electron microscope to establish the p ossible correlation between adhesion-associated shape alterations and [Ca2+]i changes. We found that 1) there was no immediate [Ca2+]i eleva tion on platelet adhesion: 2) [Ca2+]i increased in most adherent plate lets with a lag time ranging 10 to 200 s, averaging about 1 minute; 3) the pattern of [Ca2+]i changes varied drastically among individual ad herent platelets; 4) the degree of [Ca2+]i elevation appeared to corre late with the extent of morphology change, with the vast majority (>90 %) of spread platelets showed detectable [Ca2+]i changes; 5) neither m orphological nor [Ca2+]i changes correlated with the lag time; 6) plat elets treated with dimethyl-BAPTA (15 mu mol/L) underwent normal shape change without [Ca2+]i elevation; 7) cytochalasin D (10 mu mol/L) inh ibited both shape change and [Ca2+]i elevation; 8) colchicine (1 mmol/ L) was ineffective in both regards. We conclude that although platelet adhesion-associated shape changes may be accompanied with heterogeneo us [Ca2+]i changes that are microfilament-dependent, [Ca2+]i changes d o not happen immediately after platelet-surface contact and they are n ot required for adherent platelets to undergo postcontact morphologica l changes. (C) 1996 by The American Society of Hematology.