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Ca⁺-Stimulated Exocytosis in Maize Coleoptile Cells

Jens-Uwe Sutter, Ulrike Homann and Gerhard Thiel
The Plant Cell
Vol. 12, No. 7 (Jul., 2000), pp. 1127-1136
DOI: 10.2307/3871260
Stable URL: http://www.jstor.org/stable/3871260
Page Count: 10
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Abstract

Changes in membrane capacitance $(C_{{\rm m}})$ after photolysis of the caged Ca2+ compound dimethoxynitrophenamine were studied in protoplasts from maize coleoptiles. Changes in C m values resulting from increased concentrations of free Ca2+ in the cytoplasm ([ Ca2+] cyt) were interpreted as representing changes in $[{\rm Ca}^{2+}]_{{\rm cyt}}\text{-sensitive}$ exocytosis and endocytosis. A continuous increase in [ Ca2+] cyt resulted in a sigmoidal increase in C m values with a half-maximal concentration at ∼1 μM. The steep increase in C m values was followed by a variable slow phase in changing C m values. When [ Ca2+] cyt increased at a rate of $0.6\ \mu {\rm mol}\ {\rm L}^{-1}\ {\rm sec}^{-1}$, the initial steep increase in C m values lasted ∼5 to 10 sec. During this time, protoplasts increased in surface area by ∼2.5%. The biphasic dynamics of $[{\rm Ca}^{2+}]_{{\rm cyt}}\text{-stimulated}$ increases in C m values can be described by a kinetic model containing two pools of vesicles with two $[{\rm Ca}^{2+}]_{{\rm cyt}}\text{-sensitive}$ steps in the exocytotic pathway.

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