Table 1.

Comparative analysis of pharmacological properties of traditional GABA-A ionophore blockers (+ present, − absent, ? unclear or conflicting effects)

Properties	P	BPH	BL	PTZ	PC	LA
Character of channel blockage:
Competitive	−/+	−	−/+	+?	−?	+
Reversible	+	+	+	+	+	+
Voltage-dependent	+?*	+	+	+	−	+
Binding to closed channel	+	+	+		+?	+
Effects of channel state:
open frequency		−		−	+
open duration	−	−		−	−
closed frequency	+	+
closed duration	+	+		+	+
Molecular (structural) similarity:
Similarity to P	+	+	+	+	+
Similarity to other ligands	BL,PTZ, BPH		PTZ	PC,BL	LA, PTZ	PC
Ability to displace BPH	+	+	+	+
Hydrophobic molecule	+	+		−	−
Ability to inhibit GABA agonists binding	−	−	−	−	−	+
References	(I)	(II)	(III)	(IV)	(V)	(V,VI)

P – picrotoxin, BPH – bicyclophosphates, BL – butyrolactones, PTZ – pentylenetetrazole, PC – penicillin, LA – other lactam antibiotics.

^*Several studies have shown that picrotoxin inhibition of the channel may be voltage-dependent (Newland and Cull-Candy, 1992; Yoon et al., 1993; Lynch et al., 1995; Yakushiji et al., 1987).

References: I (Newland and Cull-Candy, 1992), II (Hamann et al., 1990; Maksay et al., 1996; Sinkkonen et al., 2001), III (Holland et al., 1990, 1991, 1993; Maksay et al., 1994; Mathews et al., 1996), IV (Squires et al., 1984; Maksay et al., 1994; Huang et al., 2001), V (Akaike et al., 1987; Yakushiji et al., 1987; Twyman et al., 1992; Fujimoto et al., 1995; Behrends, 2000; Lindquist et al., 2004), VI (Fujimoto et al., 1995; Sugimoto et al., 2003).