Along with heat, bacterial cells are treated with its chloride to make them competent, allowing the uptake of free plasmids.  
This substance binds to synaptotagmin to stimulate the SNARE-mediated fusion of synaptic vesicles to the cell membrane.  Along with heat, bacterial cells are treated with its chloride to make them competent, allowing the uptake of free plasmids.  In the slow mechanism for blocking polyspermy of sea urchins, the fusion of the first sperm triggers an increase in cytoplasmic concentrations of this (*) ion that allows the vitelline layer to block subsequent sperm.  It causes a conformational change in troponin C after this ion is released from the sarcoplasmic reticulum, opening up binding sites on myosin. For 10 points, name this ion important in muscle contraction which, which along with phosphate ions, forms hydroxyapatite, the primary mineral in bone.
This substance binds to synaptotagmin to stimulate the SNARE-mediated fusion of synaptic vesicles to the cell membrane.  
{calcium} ions [accept {Ca2+} or {Ca++}]