135 USE OF PURINE NUCLEOTIDE AND NUCLEOSIDE METABOLISING ENZYMES AS TOOLS TO DETERMINE THE PRESENCE OF PURINERGIC NERVE TRANSMISSION IN SMOOTH MUSCLE

It is likely that an exogenously applied enzyme can access the synaptic region and can be used to examine the role of its substrate as a neurotransmitter provided that the end product has reduced activity in the tissue. In guinea-pig ATP has been suggested as the neurotransmitter mediating relaxation by the non-adrenergic, non-cholinergic (NANC) nerves in the taenia coli and as a cotransmitter mediating the twitch component of the contraction in response to sympathetic nerve stimulation in the vas deferens. Nucleotide pyrophosphatase converts ATP to a much less active AMP and caused a significant reduction in the relaxations to NANC nerve stimulation in the taenia and to the twitch components of contractions to sympathetic nerve stimulation in the vas deferens. The enzyme failed to affect responses to noradrenaline and adrenergic neurotransmission in each tissue demonstrating its specificity. In the guinea-pig trachea adenosine has been suggested as the neurotransmitter in NANC inhibitory nerves. In dipyridamole treated preparations; adenosine deaminase caused a significant reduction in inhibitory responses to NANC nerve stimulation and to adenosine wherease responses to VIP and cholinergic nerve stimulation were unaffected. Thus studies with nucleoside and nucleotide metabolising enzymes have provided support for purinergic transmission in the guinea-pig.