Certainly it has been shown many years ago by people like Gyorgy Hajnoscky that calcium release from the ER leads to depolarization in the mitochondria. When he added a bit of IP3 to the side of a long myotube he saw a wave of calcium loss from ER that followed the loss of TMRE stain in mitos. That was about 2005 and was beautiful. So yes, certainly the oscillations can be coupled. Just not so far directly with the frequency of neurotransmitter release.