Ca2+-induced exocytosis in individual human neutrophils: high- and low-affinity granule populations and submaximal responses.
We have investigated Ca2+-induced exocytosis from human neutrophils using the whole cell patch-clamp capacitance technique. Microperfusion of Ca2+ buffer solutions (<30 nM to 5 mM free Ca2+) through the patch-clamp pipette revealed a biphasic activation of exocytosis by Ca2+. The first phase was characterized by high affinity (1.5-5 microM) and low apparent cooperativity (<=2) for Ca2+, and the second phase by low affinity (approximately 100 microM) and high cooperativity (>6). Only the second phase was accompanied by loss of myeloperoxidase, suggesting that the low-affinity exocytosis reflected release of peroxidase-positive (primary) granules, while the high-affinity exocytosis reflected release of peroxidase-negative (secondary and tertiary) granules. At submaximal Ca2+ concentrations, only a fraction of a given granule population was released. This submaximal release cannot simply be explained by Ca2+ modulation of the rate of exocytosis, and it suggests that the secretory response of individual cells is adjusted to the strength of the stimulus. The Ca2+ dependence of the high- and low-affinity phases of neutrophil exocytosis bears a resemblance to endocrine and neuronal exocytosis, respectively. The occurrence of such high- and low-affinity exocytosis in the same cell is novel, and suggests that the Ca2+ sensitivity of secretion is granule-, rather than cell-specific.
Nüsse
O
O
Division of Infectious Diseases, University Hospital Geneva, 1211 Geneva 14, Switzerland. nuesse@dminov1.hcuge.ch
Serrander
L
L
Lew
D P
DP
Krause
K H
KH
D002118:Calcium / Q000032:analysis / Q000502:physiology*; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D006801:Humans; D009504:Neutrophils / Q000166:cytology*; D018408:Patch-Clamp Techniques; D009195:Peroxidase / Q000032:analysis
D009195:Peroxidase; D002118:Calcium