Intrinsic optical and passive electrical properties of cut frog twitch fibers.

Abstract

This article describes a new apparatus for making simultaneous optical measurements on single muscle fibers at three different wavelengths and two planes of linear polarization . There are two modes of operation : mode 1 measures the individual absorbances of light linearly polarized along and perpendicular to the fiber axis, and mode 2 measures retardation (or birefringence) and the average of the two absorbance components . 89 :41-143), was routinely employed so that all our cut fiber results would be comparable. A simple method, which does not require microelectrodes, allowed continual estimation of a fiber's membrane (r ,) and internal longitudinal (r) resistances as well as the external resistance (re) under the Vaseline seals . The values of r , and r; obtained from cut fibers with this method agree reasonably well with values obtained from intact fibers using microelectrode techniques . Optical measurements were made on resting and action potential-stimulated fibers . The intrinsic fiber absorbance, defined operationally as logo of the ratio of incident light to transmitted light intensity, was similar in intact and cut preparations, as were the changes that accompanied stimulation . On the other hand, the resting birefringence and the peak of the active change in cut fibers were, respectively, only 0.8 and 0.7 times the corresponding values in intact fibers . Both the amplitude and the half-width of the active retardation signal increased considerably during the time course of cut fiber experiments ; a

Simultaneous monitoring of changes in magnesium and calcium concentrations in frog cut twitch fibers containing antipyrylazo III.

“…Optical measurements were made with a 50-am diameter spot of light focused on the middle of the fiber in the central-pool region. The intensity of transmitted light was measured simultaneously at three different wavelengths and two planes of linear polarization with the apparatus described in Irving et al (1987). Details concerning the experimental method and the processing of optical records are given in that paper and in Maylie et al (1987b, c).…”

“…16, C and D, respectively, from Baylor et al, 1986). Therefore, the average value, -15 mM, was used to estimate changes in free [Mg] inside our cut fibers in which the value of resting free [Mg] is assumed to be equal to that in the internal solution, 1 mM (Table I of Irving et al, 1987).…”

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

“…For protonated and nonprotonated indicator, a small correction was applied to the value of 8(480) to allow for the slight difference between the wavelength of light passed by the 480-nm filter and the exact isosbestic wavelength of phenol red in a calibration solution. Additional information about the determination of Aina (h) and indicator concentration is given in Irving et al (1987) and Maylie et al (1987b). All measurements of optical absorbance are expressed as 1:2 averages of the absorbance of light linearly polarized along the fiber axis and perpendicular to the fiber axis, as described in Irving et al (1987).…”

“…Additional information about the determination of Aina (h) and indicator concentration is given in Irving et al (1987) and Maylie et al (1987b). All measurements of optical absorbance are expressed as 1:2 averages of the absorbance of light linearly polarized along the fiber axis and perpendicular to the fiber axis, as described in Irving et al (1987).…”

Resting cytoplasmic free Ca2+ concentration in frog skeletal muscle measured with fura-2 conjugated to high molecular weight dextran.

“…We first considered the fiber's intrinsic absorbance. At shorter wavelengths, the fiber's absorbance is larger, so some fraction of excitation light should be absorbed by the fibers (Baylor, Chandler, and Marshall, 1982;Irving, Maylie, Sizto, and Chandler, 1987). For this purpose, the light intensity transmitted through muscle fibers was measured before the injection of fura dextran, and the intrinsic absorbance of the fiber was calculated, as described previously (see Fig.…”