Quantitative elemental x-ray imaging of timed calcium displacement from stores (JSR) in isolated single frog skeletal muscle fibers: Its efficacy in quantitation

Abstract

We are performing a continuing series of experiments to describe the time course of fast physiological events in terms of morphology and microtopochemistry, using electron probe x-ray microanalysis in both the static probe (STP) and quantitative digital imaging (QDI) modes. As a model, we are using timed spatial displacements of elements (e.g. the release of calcium from JSR) during the process of excitation-contraction coupling in single, intact skeletal muscle fibers quick-frozen at known time intervals following electrical stimulation. There is considerable variance in the total calcium concentration ([Ca]t) among JSRs, which increases the requirement for widespread sampling to increase statistical confidence. Even at a low number of pixels/raster chosen for time economy, QDI seems well suited to deal with this variance because it covers a large number of JSRs in a reasonably short scanning time (64x64 pixels: ∽3 h; 128×128 pixels: ∽9 h). Here, we report on the efficacy of QDI in our experiments and compare the results with those obtained from STP.