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Intracellular Ca
2+
dynamics in
Xenopus
melanotropes (pseudocolor)
Calcium ions-dependent signaling and homeostasis in cells
Many processes in animal as well as plant cells are steered by temporary elevations of the intracellular concentration of calcium ions ([Ca
2+
]). Examples of such processes are the contraction of muscles, the release of hormones and neurotransmitters, the movement of guard cells in leaves, and the activation or, on the contrary, inactivation of expression of certain genes. The standard [Ca
2+
] in the serum around cells in vertebrate and humans is about 1 mmol/L, whereas the concentration within the cells is 10.000 to 100.000 times lower. Cells can raise their intracellular [Ca
2+
] by inflow of Ca
2+
over the cell membrane according to strictly regulated mechanisms. A 100-fold raise in [Ca
2+
] compared to the ground state can occur within a few milliseconds.
Scientists want to measure the [Ca
2+
] within living cells to better understand the mechanisms behind Ca
2+
signaling and -homeostasis in cells. Therefore, they often use chemicals like fura-2, which chemically bind to Ca
2+
and emit fluorescence light with a variable intensity depending from the [Ca
2+
] in the cell. The movie shows such a "real-time" dynamic measurement of the fura-2 fluorescence as an indicator for the [Ca
2+
] in a melanotrope cell of the South African clawed toad (
Xenopus laevis
). Melanotrope cells, which originate from the middle lobe of the pituitary, deliver hormones that allow frogs and toads to adapt their color to the environment. The intracellular [Ca
2+
] rise that is required for delivery of hormones happens in sudden upstrokes, called steps. The movie shows a number of such steps, characterized by strong changes in color. (A low [Ca
2+
] is represented by a blue/green color, a standard concentration by a yellowish color and a high concentration by an orange/red color). In absence of Ca
2+
spikes the [Ca
2+
] diminishes again progressively because Ca
2+
is actively pumped out of the cell. A long lasting high [Ca
2+
] happens to be toxic for cells.
Research: W. Scheenen, Department of Cellular Animal Physiology.
Imaging/web text
: Department of General Instrumentation (E. Pierson, B. van der Linden).
last modified: 5 Jun 2014
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