Elementary Ca2+ release events in mammalian skeletal muscle: effects of the anaesthetic drug thiopental
- 45 Downloads
We examined the effect of clinically relevant doses of thiopental (10–100 µM) on Ca2+ release from the sarcoplasmic reticulum of chemically skinned skeletal muscle fibres of the mouse. Elementary Ca2+ release events (ECRE) were recorded with confocal microscopy and were detected and analysed by an automated algorithm. Thiopental at 25 µM evoked a marked increase in ECRE frequency (events/100 µm/s) from 0.64 ± 0.32 to 1.56 ± 0.38 (P < 0.001). Incubation with 5 µM ryanodine significantly reduced spontaneous and evoked ECRE frequencies to 0.08 ± 0.08 (P < 0.001) and 0.39 ± 0.25 (25 µM thiopental, P < 0.001) respectively. Thiopental-evoked ECRE show different morphological characteristics compared to spontaneous events. Maximum relative amplitudes (ΔF/F 0)max and spatial width (full width at half maximum) of the events were substantially increased. Full duration at half maximum was increased and some very long events (200 ms compared to ∼30 ms standard) were produced. The rise times as an indicator of the channel open time were slightly increased. Furthermore, the occurrence of repetitive ECRE was observed. These events, in contrast to previous observations in amphibian skeletal muscle fibres, displayed a multitude of different release patterns. In particular, a repetitive ECRE mode with successively decaying amplitudes was identified and the inter-event intervals were analysed. Estimation of the underlying Ca2+ release current suggests that during repetitive events with a decaying amplitude a decreasing amount of Ca2+ was released within the individual release event. Possible underlying mechanisms are discussed. In summary, thiopental seems to be a potent RyR1 agonist and substantially alters the gating mechanisms of RyR Ca2+ release channel clusters already in clinically relevant doses, i.e. doses administered during general anaesthesia.
KeywordsSkeletal muscle Calcium sparks Elementary calcium release events Thiopental
Unable to display preview. Download preview PDF.
This work was partially supported by a grant from the Ministry of Science, Research and the Arts of Baden-Württemberg, Germany - LFSP biomimetic models of cell mechanics 24-7532.22.19-12/1.
- Izu LT, Wier WG, Balke CW (1998) Theoretical analysis of the Ca2+ spark amplitude distribution. Biophys J 75:1144–1162Google Scholar