In the blowfly Protophormia terraenovae taste information is carried to the CNS by a spike activity whose frequency is directly correlated to receptor potential amplitude [1, 2].

This study investigates, in the labellar chemosensilla, whether spike frequency can be modulated independently from the receptor potential amplitude, by way of the KV channel inhibitor, 4-aminopyridine (4-AP; [1]).

By means of the extracellular side-wall technique [2], the receptor potential and the spike activity were simultaneously recorded after stimulation with NaCl (50÷500 mM), sucrose (10÷500 mM) and quinine HCl (0.1÷10 mM), before, 5 and 10 min after apical or basolateral administration of 4-AP (1÷20 mM).

The results show that the receptor potential in the "salt", "sugar" and "deterrent" cells, respectively evoked by NaCl, sucrose or quinine HCl stimulations, is not affected by 4-AP, except for the basolateral highest dose of 4-AP and at the longest interval (10 min), where the "salt" cell receptor potential amplitude is also decreased.

Instead, spike activity is significantly decreased in a dose-dependent manner for the "salt" and "sugar" cells and in a time-dependent mode for the "deterrent" cell for all 4-AP concentrations.

In conclusion, our data suggest that in the blowfly spike activity of the 3 considered cells can be modulated without changing the relative receptor potential amplitudes.

References 

1.Masala C et al. (2009) J Comp Physiol A 195:1141–1151

2.Morita H (1992) Zool Science 9:1–16