Nucleotides are naturally occurring chemicals present in all living cells, where they have defined biochemical and physiological roles. The most abundant nucleotide is adenosine 5'-triphosphate (ATP), which occurs in millimolar concentrations in the cytosol and at much higher concentrations in intracellular vesicles that serve as stores for neurotransmitters. 

Inside the cytosol, intracellular ATP represents the major energy currency for biochemical metabolism. Released from the cytosol or from storage vesicles, extracellular ATP represents a way for cells to talk to each other.  ATP and its derivatives activate a large number of membrane-bound signalling proteins, collectively called the purinoceptor family. All cells possess purinoceptors and usually more than one subtype.  As a result, these receptors affect practically every aspect of human physiology.

Dr King works on the signalling properties of the mammalian purinoceptor family, mainly by expressing purinoceptors in isolation in host cells (Xenopus oocytes or 1321N1 human astrocytoma cells). Sometimes, two or more receptor subunits are expressed together to make heteromeric assemblies of signalling molecules. Occasionally, purinoceptors are co-expressed with other types of signalling proteins to investigate receptor-receptor crosstalk. Already, he and his colleagues have studied how purinoceptors affect TRPV1, ENaC and AQP2 channels.

The results of these experiments are compared with results from parallel studies of tissues and organs containing known examples of the purinoceptor family. Dr King works closely with other scientists at UCL, to model signalling systems which employ purinoceptors and to investigate unresolved issues in human physiology.

Some of his past studies have focussed the role of extracellular nucleotides in i) bone modelling and osteoporosis, ii) control of breathing, iii) tubule function in kidney, iv) blood platelet function in control of bleeding, v) astrocyte growth following brain injury, vi) signalling in sensory nerve pathways, including the ear, vi) control of the urinary bladder and vii) control of gastrointestinal motility.
 
Recently, Dr King's attention has returned to the "gut-brain axis", and the control of appetite and satiety by purinergic transmission in motor & sensory nerve pathways connecting the brain to the GI tract.