A platelet aggregometer was adapted for the simultaneous measurement of perpendicular light scattering in addition to light transmission. The addition of chemoattractants to polymorphonuclear leukocyte suspensions evoked a single wave of increased light transmission, whereas the perpendicular scattering measurement demonstrated a previously unrecognized biphasic response. The first perpendicular scattering response had no detectable latency and peaked at 10 +/- 1 s, then decayed rapidly. The second response peaked at 40 +/- 5 s, and decayed over several minutes. The dose-response curve of chemoattractants for inducing the rapid (10 +/- 1 s) perpendicular scattering peak corresponded to that which initiated chemotaxis. Initiation of the slow (40 +/- 5 s) peak required 10-fold higher amounts of chemoattractants, and the dose-response curve correlated with the induction of lysosomal enzyme secretion and superoxide anion production. Low doses of aliphatic alcohols, which have been shown to enhance chemotaxis but to inhibit secretion and superoxide anion production, abolished the slow perpendicular light-scattering response but left the fast response intact. Stimulants of secretion induced only slow and prolonged responses that were best observed in transmission measurements. In an attempt to resolve the origin of the light-scattering responses, the morphological changes of polymorphonuclear leukocytes were examined microscopically. Neither aggregation nor morphological whole cell polarization could be correlated with changes in light transmission or perpendicular scattering, which suggested that the source of scattering is of subcellular dimensions. The rapid perpendicular light-scattering response of polymorphonuclear leukocytes to chemoattractants appears to record an initial event in the stimulus-response coupling, and its measurement should provide a useful new tool for the study of leukocyte function. The biphasic nature of the light-scattering responses to chemoattractants, moreover, correlates with the dual regulation of the chemotactic and secretory responses of leukocytes.
I Yuli, R Snyderman
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