Ca(2)+-stimulated exocytosis in maize coleoptile cells.
Changes in membrane capacitance (C(m)) after photolysis of the caged Ca(2)+ compound dimethoxynitrophenamine were studied in protoplasts from maize coleoptiles. Changes in C(m) values resulting from increased concentrations of free Ca(2)+ in the cytoplasm ([Ca(2)+](cyt)) were interpreted as representing changes in [Ca(2)+](cyt)-sensitive exocytosis and endocytosis. A continuous increase in [Ca(2)+](cyt) resulted in a sigmoidal increase in C(m) values with a half-maximal concentration at approximately 1 microM. The steep increase in C(m) values was followed by a variable slow phase in changing C(m) values. When [Ca(2)+](cyt) increased at a rate of 0.6 micromol L(-)(1) sec(-)(1), the initial steep increase in C(m) values lasted approximately 5 to 10 sec. During this time, protoplasts increased in surface area by approximately 2.5%. The biphasic dynamics of [Ca(2)+](cyt)-stimulated increases in C(m) values can be described by a kinetic model containing two pools of vesicles with two [Ca(2)+](cyt)-sensitive steps in the exocytotic pathway.
Sutter
J U
JU
Albrecht-von-Haller Institute for Plant Sciences, Plant Biophysics, Göttingen, Germany.
Homann
U
U
Thiel
G
G
D002118:Calcium / Q000378:metabolism*; D005089:Exocytosis; D007700:Kinetics; D008564:Membrane Potentials; D003313:Zea mays / Q000166:cytology / Q000378:metabolism* / Q000502:physiology
D002118:Calcium