The first real research I did was as a M.Sc. student in Joop van Zoelen's lab (1991). He had just started a new research lab in Nijmegen in Cell Biology with as a main topic 'growth factors cellular growth'. Polypeptide growth factors bind to a receptor in the plasma membrane that will tranduce a signal, the second messenger. In my case we were interested in the cleavage of membrane lipids. In this pathway, inositon 3 phosphate is released when a certain lipid PIP2 was chemically cleaved. My first assignment was to set up an IP3 assay based on the method described in Ben Tilly's thesis.The experimental setup was relatively simple. You let the cells grow in the presence of radioactive inositol, so that it will be incorporated into membrane lipids. After incuabting the cells with normal medium for a while, you add growth factors and you measure how much radioactive inositol is released from the lipids, just by measuring radioactivity in the aqeuous fraction. When performed neatly, the assay was very sensitive and reproducible. Even though duplicates were always used, the values were so close to each other that it was hardly necessary to take duplicates. The assay was used by me and results used for several articles. Bradykinin and LPA were strong inducers of this pathway. Inhibition and stimulation of cell growth by growth factors could be studied at the level of the IP3 second messenger and others. All in all a nice assay, that could complement other cell growth assays such as radioactive DNA incorporation