I'm not sure whether this will work for your purposes, but I've done it many
to measure intact cell cyclic AMP accumulation assays. Many cells will take
up adenine from surrounding medium , and some proportion of it will become
incorporated into the ATP pool. We used this in order to measure the con-
version of ATP to cAMP by adenylyl cyclase without having to rupture the cell.
We commonly incubated cells with low mM concentrations of adenine with a 3H-
spike thrown in to monitor product accumulation (adenine, ATP, and cAMP can
be separated on alumina columns). Hope this helps.