Lamboley, Cedric ORCID: 0000-0002-4008-4929 and Pape, Paul C (2011) The concentration of free Ca 2+ in the sarcoplasmic reticulum of frog cut twitch skeletal muscle fibers estimated with tetramethylmurexide. Cell Calcium, 50 (6). pp. 530-547. ISSN 0143-4160

Abstract

The contractile response in skeletal muscle is controlled by the time course and magnitude of Ca2+ release from the sarcoplasmic reticulum (SR) into the myoplasm. In order to gain an understanding of how SR Ca2+ release is regulated, it is often useful to estimate the permeability of the SR to Ca2+ as this provides a measure of the extent of activation of SR Ca2+ release channels. The permeability of the SR is proportional to the rate of Ca2+ release normalized by the driving force for release which is primarily determined by the concentration of free calcium in the SR (denoted [Ca2+]SR). In past studies (e.g. [1–4]), the driving force for Ca2+ release was taken to be the concentration of total calcium in the SR (denoted [CaT]SR) rather than [Ca2+]SR owing to the lack of information about [Ca2+]SR. The primary aims of the experiments in this article were to establish the resting value of [Ca2+]SR (denoted [Ca2+]SR,R) with the absorbance indicator tetramethylmurexide (TMX) and, perhaps more importantly, the ratio of [Ca2+]SR,R and TMX’s apparent dissociation constant. This latter information is needed to establish the time course of [Ca2+]SR with TMX during SR Ca2+ release and, thereby, the time course of the true release permeability.

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