Figure 4. Modulation of ECRE frequency in adult mammalian muscle.

In A, the effect of 0.5 mm caffeine on the event frequency in a chemically skinned mammalian and a chemically skinned amphibian fibre is demonstrated in two representative x–y images (70 μm × 50 μm). The mean number of events per image in a xyt-series in these two representative fibres increased from 1.24 ± 0.17 (20 images, mammalian) and 2.23 ± 0.19 (50 images, amphibian) under control conditions to 3.42 ± 0.28 (80 images, mammalian) and 4.78 ± 0.53 (50 images, amphibian) in the presence of caffeine. B, the frequency of ECRE observed in a representative chemically skinned mammalian fibre exposed to a free intracellular Mg²⁺ concentration of 0.4 mm (3.58 ± 0.16 events per image, 100 images) was comparable with that observed in a chemically skinned mammalian fibre in 1 mm free Mg²⁺ (3.54 ± 0.14 events per image, 100 images), showing that 1 mm free intracellular Mg²⁺ was not a limiting factor for the observation of ECRE in skinned fibres. C, the frequency of ECRE was reduced from 1.18 ± 0.18 (100 images) to 0.31 ± 0.05 (100 images) upon application of 2 mm tetracaine in a representative chemically skinned mammalian fibre.