Cytosolic Ca2+ concentrations typically rise about 50-fold when Ca2+ channels open in the plasma membrane. Assume that 1000 Ca2+ channels open in a cell with a volume of 1000 µm3 and an internal Ca2+ concentration of 100 nM. If each Ca2+ channel passes 106 Ca2+ ions per second, how long would the channels need to stay open in order to raise the intracellular Ca2+ concentration to 5 µM?