Fig. 2.

Inhibition of ACh-evoked currents from neuronal and muscle-type nAChRs by the phycotoxins. SPX with human α4β2 expressed in oocytes (A and B); GYM with Torpedo α1₂βγδ incorporated into the oocyte membrane (C and D). (A and C) Typical inward nicotinic currents evoked by a 5-s perfusion of 150 μM ACh (EC₅₀ value for α4β2) before and after application of 1.5 nM SPX (A), and a 7-s perfusion of 25 μM ACh (EC₅₀ value for α1₂βγδ) before and after application of 1.5 nM GYM (C). The desensitization component typical of α1₂βγδ is not modified in presence of the toxin. (B and D) SPX (B) and GYM (D) concentration-to-current inhibition relationships. The amplitudes of the ACh-induced currents recorded in the presence of SPX and GYM (mean ± SEM; 3–4 oocytes per concentration) were normalized to control currents and fitted to the Hill equation. SPX on α4β2: IC₅₀ = 3.87 ± 1.1 nM; nH = 1.9 ± 0.33; GYM on α1₂βγδ: IC₅₀ = 2.8 ± 1.15 nM; nH = 0.96 ± 0.15 (compare Table 2).