In skinned cells, this can be detected as a depletion of t-tubule Ca2+ following activation of RyR1 [18].
Most importantly, effective Ca2+ concentrations available to induce myosin activity are clearly different and optimal for skinned cells causing maximum contractions in those cells.
As described previously [11], in the absence of cytocolic Cl−, which normally serves to stabilize the membrane potential, some skinned cells exhibit spontaneous depolarisations, resulting in repeated twitch-like responses.
Mechanically skinned cells are prone to spontaneous depolarisation of the t-tubule network [11], and although such events can induce substantial intracellular Ca2+ transients (Fig. 6B), it seems likely that subthreshold depolarisations also occur.
In contrast, the membrane of skinned muscle cell segments is removed, chemically or mechanically, allowing the myofilament environment to be controlled from the bath fluid.
It was shown, that after degradation of these proteins by low doses of ionizing radiation, the ability of single skinned muscle cells to generate both passive tension in response to stretch and active tension in response to calcium was greatly reduced [ 58].
UV radiation is a known carcinogen and excessive exposure increases the risk of lip, skin basal cell and squamous cell carcinomas and cutaneous melanoma, particularly in fair-skinned population.
Permeabilized cells or skinned muscle fibre preparations can be considered as a subset of isolated mitochondria, with similar strengths and weaknesses.
Non-melanoma skin cancer (NMSC) is the most frequent cancer type in fair-skinned populations and includes basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) (Madan et al, 2010).
Compared with skinned heart-muscle fibres or cells [ 66- 69], in which the surface membrane has been permeabilized, our preparations kept the intracellular environment intact, thus avoiding the possibility that myofibrillar Ca2+ sensitivity was affected by perturbations in the intracellular environment.
