Intracellular application of polyamine and polyamine amide inhibits the quisqualate-sensitive ionotropic glutamate receptor of locust (Schistocerca gregaria) muscle

The effects of intracellularly-applied philanthotoxin-343 (PhTX-343) on single channel currents gated by quisqualate-sensitive glutamate receptors (qGluR) of locust leg muscle have been studied. PhTX-343 initially increased qGluR channel open probability, mainly by virtue of an increase in mean channel open time, but this was followed by a decrease in channel open probability, sometimes to zero, because of a decline in the frequency of channel openings and a decline in mean channel open time. These results suggest that antagonism of qGluR by PhTX-343 can arise, in part, through binding of the toxin to a site or sites on the intracellular domain of this receptor.