Ca2+-induced exocytosis in individual human neutrophils: high- and low-affinity granule populations and submaximal responses

Nüße, Oliver; Serrander, Lena; Lew, Daniel P.; Krause, Karl-Heinz
March 1998
EMBO Journal;3/1/98, Vol. 17 Issue 5, p1279
Academic Journal
We have investigated Ca2+-induced exocytosis from human neutrophils using the whole cell patch­clamp capacitance technique. Microperfusion of Ca2+ buffer solutions (<30 nM to 5 mM free Ca2+) through the patch­clamp pipette revealed a biphasic activation of exocytosis by Ca2+. The first phase was characterized by high affinity (1.5–5 μM) and low apparent cooperativity (≤2) for Ca2+, and the second phase by low affinity (∼100 μM) 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 peroxidase­negative (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.


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