The effects of the intracellular Ca2+ concentration ([Ca2+]i) and a nonhydrolyzable guanosine triphosphate, guanosine 5′-o-(3-thiotriphosphate) (GTP-γ-S), on secretion were studied by a patch-clamp technique in human basophils. When 10 μM Ca2+ were applied intracellularly, the granules dispersed rapidly, moved vigorously and fused to the cell membrane in 5 min. When the cells were exposed to 2 μM [Ca2+]i and 100 μM GTP-γ-S, the granules dispersed gradually and granule fusion continued for 7–10 min. The plasma membrane conductance did not appreciably change with either 10 μM [Ca2+]i alone or 2 μM [Ca2+]i + 100 μM GTP-γ-S. Intracellular application of Ca2+, 1–10 μM, caused a dose-dependent increase in cell membrane capacitance, which reflects granule membrane fusion, indicating exocytosis in a Ca2+ concentration-dependent manner. The addition of 100 μM GTP-γ-S promoted an increase in the plasma membrane capacitance at concentrations from 0.1 to 2 μM [Ca2+]i and at 2 μM [Ca2+ ]i the increase was 4.4 times greater than that with 2 μM [Ca2+]i alone. These results indicate that certain G protein(s) promote Ca2+-dependent exocytosis in human basophils.

Keywords:
Basophils, human, Exocytosis, Patch-clamp technique, Bronchial asthma, G protein
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© 1997 S. Karger AG, Basel
1997
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