[7] Initially intending to return to Southern Rhodesia (now Zimbabwe) after his PhD, Berridge's plan was thwarted by the Rhodesian Bush War.
[7] In 1969, John Treherne invited Berridge to return to the University of Cambridge and join the new Unit of Invertebrate Chemistry and Physiology that he was setting up in the Department of Zoology.
[11] Working on the salivary glands of a blow fly species, Berridge showed cyclic AMP produced the same physiological effect as serotonin, dramatically increasing saliva secretion.
This suggested cyclic AMP caused positively-charged ions to move across the epithelium from the extracellular fluid to the inside of the salivary gland (known as the lumen).
[13] Berridge suspected calcium ions (Ca2+) could explain the distinct electrical but similar physiological effects of serotonin and cyclic AMP.
With help from Rex Malcolm Chaplin Dawson, who was studying inositol at the Babraham Institute near Cambridge, Berridge found that phosphatidylinositol was hydrolysed into IP3 and DAG.
[18] This report, together with Yasutomi Nishizuka's discovery that DAG was a second messenger in its own right and could activate protein kinase C,[19] marked the start of the field of calcium signaling.