Apparent opposing effects of cyclic AMP and dibutyryl cyclic GMP on the neuronal firing of the blowfly chemo-receptors.

Cyclic AMP and its dibutyryl derivative inhibit neuronal firing of the labellar sugar sensitive receptor of the blowfly when applied in conjunction with the stimulant sucrose. Furthermore, simultaneous application of aminophylline (phosphodieterase inhibitor) and sucrose or in combination with cyclic AMP caused a similar depression of the sugar receptors response. In contrast, dibutyryl cyclic GMP elicited an increase in sugar receptor firing when applied with sucrose to sugar receptor. Either 5'-AMP or 5'-GMP in combination with sucrose had no discernable effect on the sugar receptors response. Different ratio combinations of cyclic AMP and dibutyryl cyyclic GMP showed the striking inhibitory effect of cyclic AMP upon the dibutyryl cyclic GMP elicited increases in receptor firing frequency. Therefore, it is suggested that these two nucleotides may be mediating different but complimentary aspects of sugar receptor function in a push-pull manner.