Effect of Energy Depletion and Antimicrobial Peptides on Single Protein Motility in Living Escherichia coli

Abstract

Store-operated Ca 2þ entry (SOCE) is a mechanism that allows the entry of Ca 2þ upon depletion of the internal stores. The skeletal muscle cell is built for the rapid delivery of Ca 2þ to the contractile proteins. The cell microarchitecture allows this with the surface membrane invaginating into the cell forming the tubular (t-) system which apposes the sarcoplasmic reticulum (SR) for rapid signalling. In skeletal muscle SOCE has been shown to occur within 1 s of Ca 2þ release (Launikonis & Rios, 2007) but this should be significantly faster if the molecular agonists are prepositioned for activation. To examine SOCE kinetics we used skinned fibres from C57 mice (7-20 weeks old) with t-system trapped fluo-5N, bathed in an internal solution with 50 mM rhod-2. These dyes were simultaneously imaged in xyt mode on a confocal microscope (2 ms/line) while Ca 2þ release was induced by lowering [Mg 2þ ]. Global Ca 2þ release induced SOCE activation and deactivation as the Ca 2þ store refilled upon release inactivation (Launikonis & Rios, 2007). We also observed Ca 2þ waves in the continued presence of low Mg 2þ . These waves allowed an accurate observation of the latency between SR Ca 2þ release and SOCE. Thus SOCE ''coupling delay'' following the initiation of SR Ca 2þ release was determined to be 27 5 4 ms (n ¼ 6).