Altered Calcium-Induced Exocytosis in Neutrophils from Allergic Patients

Abstract

We have investigated the exocytotic characteristics of neutrophils from allergic patients and healthy volunteers employing the whole cell membrane capacitance (Cm) measurement. The mean serum IgE level from allergic patients (423.75 ± 12.75 IU/ml) determined by chemiluminescence immunoassay was much higher than that of healthy volunteers (28.47 ± 16.68 IU/ml). Intracellular dialysis of buffered Ca²⁺ and GTPγS triggered biphasic exocytosis. The total capacitance increment displayed a steep dependence on pipette free Ca²⁺ concentration ([Ca²⁺]_p), with maximal stimulation achieved at 10 µM. A significant decrease in the total capacitance increment was observed in the allergic group at [Ca²⁺]_p >10 µM. Moreover, at submaximal stimulatory [Ca²⁺]_p of 1 µM, the maximal rate of exocytosis in allergic patients (V_max = 20.75 ± 6.19 fF/s) was much faster than that of the healthy control group (V_max = 7.97 ± 2.49 fF/s). On the other hand, the Ca²⁺-independent exocytosis stimulated by GTPγS displayed no significant difference in either the total membrane capacitance increments or the maximal rate of exocytosis. The results suggest that hypersecretion of neutrophils in allergic diseases may involve the development of abnormal Ca²⁺-dependent exocytosis.