Table 3.

A summary of nematode GABA subunits and receptor pharmacology.

Gene	Species	Subunit	Tissue distribution	Receptor	Pharmacology
					GABA (EC50)	Picrotoxin (IC50)
unc-49	C. elegans	UNC-49A	Not known	Does not express as a functional receptor1
		UNC-49B	body wall musculature, anal sphincter muscle, dorsal nerve cord, ventral nerve cord and nerve ring1	Expresses as a homomeric channel1,2	43.7 ± 2.9 μm 1	0.9 ± 0.2 μm 2
		UNC-49C	body wall musculature, dorsal nerve cord, ventral nerve cord and nerve ring1	Does not express as a functional receptor1
				Cel-UNC-49B and Cel-UNC-49C co-assemble to form a heteromeric channel1,2	107.5 ± 13.5 μm1	166.0 ± 42.0 μm 2
	H. contortus	UNC-49B	Not determined	Expresses as a homomeric channel3,4,5	64.0 ± 4.4 μM3 76 ± 6 μm5	3.65 ± 0.64 μM4
					Agonist profile:GABA > trans-4-aminocrotonic acid (TACA) > guanidinoacetic acid (GAA) > imidazole-4-acetic acid (IMA) > isonipecotic acid > isoguvacine > β-alanine > 5-aminovaleric acid (DAVA)5
		UNC-49C	Not determined	Does not express as a functional receptor
				Hco-UNC-49B and Hco-UNC-49C co-assemble to form a heteromeric channel3,4,5	39.9 ± 5.7 μM3 59 ± 8 μm5	134.56 ± 44.12 μM4
				Agonist profile:GABA > TACA > isoguvacine > IMA > R(−)-4-amino-3-hydroxybutyric acid R(−)-GABOB > S(+)-GABOB, > GAA > isonipecotic acid > DAVA > β-alanine5
lgc-37 (hg1)	H. contortus	LGC-37A/HG1A LGC-37E/HG1E	Ventral nerve cord and in a few neurons associated with the nerve ring around the pharynx6	Does not express as a GABA sensitive homomeric receptor6,7
Gab-1	C. elegans	GAB-1	Not determined	Does not express as a GABA sensitive homomeric receptor8
				Cel-GAB-1 forms a heteromeric channel when expressed with Hco-HG1A and HG1E8	Cel-GAB-1/Hco-HG1A = 17.83 μM8	Not determined
					Cel-GAB-1/Hco-HG1E = 3.3 μM8	Not determined
lgc-38	H. contortus	LGC-38	Not known	Expresses as a homomeric channel8	19.3 ± 4.3 μM9	Not determined. 10 μM PTX produced 97.8 ± 0.9% inhibition of the 20 μM GABA response9
exp-1	C. elegans	EXP-1	intestinal and anal depressor enteric muscle10	Expresses as a homomeric channel10	26.4 ± 1.08 μM10 21.0 ± 0.7 μM11	Resistant to the channel blocking effects picrotoxin11
lgc-35	C. elegans	LGC-35	sphincter enteric muscle, a subset of ventral cord acetylcholine motor neurons and the spicule protractor in males12,13	Expresses as a homomeric channel11	17 ± 0.71 μM11	Resistant to the channel blocking effects picrotoxin11

¹Bamber et al. (1999).

²Bamber et al. (2003).

³Siddiqui et al. (2010).

⁴Brown et al. (2012).

⁵Kaji et al. (2015).

⁶Laughton et al. (1994).

⁷Skinner et al. (1998).

⁸Feng et al. (2002).

⁹Siddiqui et al. (2012).

¹⁰Beg and Jorgensen (2003).

¹¹Nicholl et al. (2017).

¹²Jobson et al. (2015).

¹³Jones and Sattelle (2008).