Changes in cytosolic calcium concentrations and cell morphology in single platelets adhered to fibrinogen-coated surface under flow

Abstract

Changes in intracellular calcium concentration [Ca2+](i) of fura-2- loaded human platelet during its adhesion to a fibrinogen-coated surface were studied, using a flow chamber mounted on an epifluorescence microscope equipped with digital-ratio imaging. Adherent platelets were individually mapped under a scanning electron microscope to establish the possible correlation between adhesion-associated shape alterations and [Ca2+](i) changes. We found that 1) there was no immediate [Ca2+](i) elevation on platelet adhesion; 2) [Ca2+](i) increased in most adherent platelets with a lag time ranging 10 to 200 s, averaging about 1 minute; 3) the pattern of [Ca2+](i) changes varied drastically among individual adherent platelets; 4) the degree of [Ca2+](i) elevation appeared to correlate with the extent of morphology change, with the vast majority (>90%) of spread platelets showed detectable [Ca2+](i) changes; 5) neither morphological nor [Ca2+](i) changes correlated with the lag time; 6) platelets treated with dimethyl-BAPTA (15 μmol/L) underwent normal shape change without [Ca2+](i) elevation; 7) cytochalasin D (10 μmol/L) inhibited 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 heterogeneous [Ca2+](i) changes that are microfilament-dependent, [Ca2+](i) changes do not happen immediately after platelet-surface contact and they are not required for adherent platelets to undergo postcontact morphological changes.