When there are multiple departure or approach frequencies depending on bearing, which one do you choose?

For Peoria, for example, the departure frequencies are 124.67 (126-304) 125.8 (305-125). Are the headings for which heading you are going, or bearings from the control tower? I'm just a little confused on this. If it is bearing from the tower then how do you know your heading from the tower? Thanks in advance?