Calcium sensitivity of petrosal ganglion neurons (PGNs) to chemical stimuli with and without PC-12 cells in co-culture instead of glomus is not known- the idea being that two types of unusual cells could form synapse and provide a model for studies of chemotransduction. Calcium levels in the PGNs were measured in the presence of different chemical stimuli in the bath medium. Remarkably, the PGNs alone were not sensitive to hypoxia (10 torr), PCO ( approximately 300 torr in normoxa) nor to ATP (100microM) but they developed the sensitivity to these stimuli in synaptic contact with PC-12 cells. The sharp rise in calcium level was suppressed (2/3) by suramin (100microM), a purinergic blocker, and the remaining 1/3 was blocked by hexomethonium, a cholinergic blocker. Taken together, these observations suggest that PGNs developed neurotransmission when in contact with PC-12 cells, as if the latter substituting for glomus cells, thus providing a model for chemotransduction studies. The reason for the insensitivity of PGNs alone to the chemical stimuli is unknown at this time.