. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. INTERACTION OF ELECTROMAGNETIC FIELDS 173. 320 400 500 EMISSION WAVELENGTH. Em (ntn) 600 Figure 4. Spectral emission from an ensemble of L929 cells illus- trating the chelation of Ca++. Each graph contains two superimposed plots, one for excitation wavelength Ex = 340 nm (solid curve), and one for E, = 380 nm (dashed curve). The large peaks at the left, centered at Em = 340 nm and Em = 380 nm, are reflections by the sample holder of the incident radiation. The small peaks (Em = 385 nm and 440 nm) are artifacts, probably Rama
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. INTERACTION OF ELECTROMAGNETIC FIELDS 173. 320 400 500 EMISSION WAVELENGTH. Em (ntn) 600 Figure 4. Spectral emission from an ensemble of L929 cells illus- trating the chelation of Ca++. Each graph contains two superimposed plots, one for excitation wavelength Ex = 340 nm (solid curve), and one for E, = 380 nm (dashed curve). The large peaks at the left, centered at Em = 340 nm and Em = 380 nm, are reflections by the sample holder of the incident radiation. The small peaks (Em = 385 nm and 440 nm) are artifacts, probably Raman scattering. The broad peaks, centered between Em = 480 nm and 500 nm, indicate the relative fluorescence emission. The cells were loaded for hours in 3 fura2AM in 3 ml of Ca-free buffer, washed three times in buffer, and mounted in a cu- vette containing 3 ml of Ca-free buffer, (a) Spectra immediately after mounting (clock time = 12:57:33); (b) The same cell ensemble 52 min- utes later (clock time 13:49:48) after again washing the cells in Hal- lam's, mounting in new cuvette with fresh buffer and CaCl:; (c) The same ensemble 23 min later (clock time 14:12:54) with mM CaCl:. The temperature was maintained at T = 37°C. of calcium channels per cell is not known, but based on the number of Na-channels (Darnell el a/., 1986), 400 is a reasonable number. Thus to reduce the cytosolic Ca++ concentration by 200 nM requires that each channel on the average transport 100 ions. Calculations based on NMR-derived rate constants for gramicidin channels (Urry et ai, 1980) suggest a conduction of 107 ions/s/ channel for a 1 Mexternal to 10~7M internal concentra- tion gradient. Thus for 10~3 M external to 10~7 M inter- nal concentration a conduction of 104 ions/s/channel would seem to be a very conservative estimate. This leads to a transient time constant of the order of milliseconds, as is observed via patch clamp techniques. A change in fluorescent intensity of the orde
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