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Calcium-Binding Protein Protocols Calcium-Binding Protein Protocols

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Monitoring Ca 2+ -Calmodulin Concentration 375<br />

Fig. 5. Estimation of the concentration of expressed indicator in HEK-293 cells<br />

using confocal microscopy as described in the text. Mean gray level values for optical<br />

sections of pure indicator solutions (�) were plotted vs the indicator concentration to<br />

establish the standard curve shown. Estimated indicator concentrations for several cells<br />

based on the mean gray level values are also plotted on the standard curve (�).<br />

insensitive to bound CaM (see Fig. 3). Emitted light passed by a D525/40 filter<br />

is detected using a photomultiplier tube.<br />

1. Cells are prepared by growing them on #1 glass cover slips to the desired density.<br />

Cover slips are then mounted in a modified Sykes-Moore chamber (Bellco Glass,<br />

Vineland, NJ) and overlaid with 1 mL of a standard HEPES buffered saline solution<br />

(HBS: 141 mM NaCl, 5 mM KCl, 1 mM MgSO 4, 10 mM glucose, 10 mM<br />

HEPES; pH 7.4). Optical sections of 8–12 cells are taken using a 15-µm scanning<br />

slit, which is optimal for the ×40 oil-immersion objective used.<br />

2. Using identical settings for gain, offset, and laser power level, optical sections<br />

are also taken in standard indicator solutions that have been sandwiched between<br />

two #1 glass cover slips mounted in a Sykes-Moore chamber.<br />

3. Emission intensity information digitized as 8-bit gray-level images is analyzed<br />

using standard image processing software, and the mean gray-level values for<br />

8–12 regions of interest are determined. We currently use a freely distributed<br />

version of NIH Image available from Scion Corporation for this purpose<br />

(Frederick, MD). Background subtractions are made using a mean gray-level<br />

value calculated based on empty regions of the cover slip.

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