Compound exocytosis of granules in human neutrophils.
Human neutrophils are of prime importance for the immune defense. Recent data from eosinophils and pancreatic beta cells have indicated that granules, upon exocytosis, occasionally fuse with each other in the cytosol prior to their subsequent fusion with the plasma membrane. This is termed compound exocytosis. We therefore studied exocytosis of single granules from human neutrophils by the high-resolution cell-attached patch-clamp capacitance technique. We found that 1.5% of the capacitance steps was greater than 5 fF, i.e., significantly larger than steps expected for exocytosis of single granules. The mean step size of these events was 20.5 fF, corresponding to compounds formed by at least five granules. The capacitance input from compound steps contributed more than 20% of the total capacitance increase. Electron microscopy captured morphological manifestations of transient exocytic events, confirming the functional results obtained by capacitance measurements. Compound exocytosis may be a mechanism for efficient targeting of release during exocytosis.
Lollike
Karsten
K
The Granulocyte Research Laboratory, Department of Hematology, Rigshospitalet, Copenhagen, Denmark. kalo@novonordisk.com
Lindau
Manfred
M
Calafat
Jero
J
Borregaard
Niels
N
D002459:Cell Fusion; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008565:Membrane Proteins / Q000097:blood; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins
D008565:Membrane Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D015759:Ionomycin