Cutting edge: Optical microspectrophotometry supports the existence of gel phase lipid rafts at the lamellipodium of neutrophils: Apparent role calcium signaling

Although much progress has been made in elucidating the biochemical properties of lipid rafts, there has been less success in identifying these structures within living cell membranes, which has led to some concern regarding their existence. One difficulty in analyzing lipid rafts using optical microscopy is their small size. We now test the existence of lipid rafts in polarized neutrophils, which redistribute lipid raft markers into comparatively large lamellipodia. Optical microspectrophotometry of Laurdan-labeled neutrophils revealed a large blue shift at lamellipodia relative to cell bodies. This blue shift disappeared after exposure to methyl-beta-cyclodextrin (mbetaCD), which disrupts lipid rafts. The Ca2+ channel transient receptor potential-like channel-1, a lipid raft marker, traffics to lamellipodia, but redistributes uniformly about cells after exposure to mbetaCD. This is accompanied by disruption of Ca2(+) waves normally initiated at lamellipodia. Thus, mbetaCD-sensitive lipid-ordered domains are present at and participate in signaling-from the lamellipodia of living neutrophils.