Arsenazo III and antipyrylazo III calcium transients in single skeletal muscle fibers.

Abstract

The metallochromic Ca indicators arsenazo III and antipyrylazo III were introduced individually into cut single frog skeletal muscle fibers from which Ca transients were elicited either by action potential stimulation or by voltage-clamp pulses of up to 50 ms in duration. Ca transients recorded with both dyes at selected wavelengths have similar characteristics when elicited by action potentials. Longer voltage-clamp pulse stimulation reveals differences in the late phases of the optical signals obtained with the 2 dyes. The effects of different tension blocking methods on Ca transients were compared experimentally. Internal application of EGTA [ethylene glycol bis (.beta.-aminoethyl ether) tetraacetate] at concentrations up to 3 mM was demonstrated to be efficient in blocking movement artifacts without affecting Ca transients. Higher EGTA concentrations affect the Ca signals'' characteristics. Differential effects of internally applied EGTA on tension development as opposed to Ca transients suggest that diffusion with binding from Ca2+ release sites to filament overlap sites may be significant. The spectral characteristics of the absorbance transients recorded with arsenazo III suggest that in situ recorded signals cannot be easily interpreted in terms of Ca concentration changes. A more exhaustive knowledge of the dye chemistry and/or in situ complications in the use of the dye will be necessary.