TRACON Controller described a loss of separation event noting the decision making process between the two controllers involved was less than required.

Narrative

Events leading up to the loss of separation are as follows; a runway change was in progress from 30's/35 to 30's/17. This slightly changed the dynamic of my airspace; thus forced me to reroute two airplanes under my control at the time. I released a MU2 off of a satellite airport and observed his tag acquire off the departure end; however I was not able to raise the aircraft on my radio frequency. After five or six miles I called the satellite airport and asked them to try and ship the MU2 again. The MU2 called me when they were about 10 to 12 miles at 2;500 FT. This in return changed the original plan for the Departure Controller to work the airplane because the MU2 was already 20 miles south of our Class B airport. After I was given the point out approval by the Departure Controller that it was my airplane to work out high; I climbed the MU2 to 12;000. Thereafter; due to our runway change; I saw it necessary to turn the MU2 from a 180 heading to a 90 heading for a brief period of time to allow for the Class B airport's arrival aircraft to descend below. The Departure Controller was working an E170 departure off the Class B airport. After passing pertinent Class B arrival traffic the Departure Controller cleared the E170 to 17;000 and at some point in the near future cleared them to a fix to join one of our SID's. I was scanning the scope and working other aircraft when I observed the conflict between these two airplanes. I was not positive what direction the E170 was turning to so I called traffic for the MU2. The MU2 saw the E170 but by this time the separation was already lost. Recommendation; the decision making process between the two controllers involved needed to be changed. I was busy enough where I didn't need to be working airplanes out of my airspace altitudes that high anyway. I have no doubt in my mind that if the Departure Controller was working both airplanes there would have been no deal.