Results
Both NFEPP and fentanyl produced dose-dependent increases in [35S]-GTPγS binding (Figure 1). The maximum effects of NFEPP were significantly higher and the EC50values were significantly lower at pH 6.5 when compared to the physiological pH 7.4 (see Table 1; *P < 0.05; pH 6.5 versus pH 7.4; t test, N=6 and 7 membranes). In contrast, fentanyl showed similar potencies (EC50) and similar maximum effects at both pH values (Figure 1, Table 1).
Table 1. EC50 values in [35S]-GTPγS binding experiments