Table 1.

Half maximal effective concentration (EC₅₀) (M) and half maximal inhibitory concentration (IC₅₀) (M) values of all tested G-protein-coupled receptors with the indicated ligands or inhibitors

EC50 (M)/IC50 (M)	Tyramine	Octopamine	Clonidine	Norepinephrine	Dopamine	Epinephrine	Yohimbine	Mianserin
Platynereis dumerilii α1-adrenergic	inactive	inactive	inactive	2.1E − 07***	1.2E − 04***	3.7E − 07 ns	4.4E − 06	3.7E − 06
95% CI				1.0E − 007 to 4.2E − 007	2.7E − 005 to 0.00056	1.3E − 007 to 1.1E − 006	2.3E − 006 to 8.2E − 006	1.9E − 006 to 7.2E − 006
P. dumerilii α2-adrenergic	8.4E − 05	2.7E − 06***	2.6E − 06	8.2E − 09***	1.6E − 06	1.1E − 08 ns	5.7E − 06	2.5E − 05
95% CI	2.8E − 005 to 0.00024	6.683E − 007 to 1.0E − 005	2.4E − 007 to 2.7E − 005	5.7E − 009 to 1.1E − 008	8.3E − 007 to 3.2E − 006	5.0E − 009 to 2.2E − 008	3.5E − 006 to 9.1E − 006	1.2E − 005 to 5.1E − 005
S. kowalevskii α1-adrenergic	inactive	inactive	inactive	1.7E − 08***	3.8E − 06***	1.9E − 08 ns	1.3E − 05	4.5E − 06
95% CI				1.0E − 008 to 2.7E − 008	1.9E − 007 to 7.4E − 005	9.0E − 009 to 4.1E − 008	7.6E − 006 to 2.2E − 005	1.6E − 006 to 1.1E − 005
S. kowalevskii α2-adrenergic	3.7E − 06	1.9E − 06	3.6E − 08	1.2E − 13***	5.6E − 09	2.3E − 09***	3.3E − 07	inactive
95% CI	2.0E − 006 to 6.8E − 006	2.5E − 007 to 1.4E − 005	6.7E − 009 to 1.9E − 007	6.7E − 014 to 1.9E − 013	3.3E − 009 to 9.4E − 009	1.1E − 009 to 4.6E − 009	2.6E − 007 to 4.0E − 007
Priapulus caudatus α1-adrenergic	inactive	inactive	inactive	7.5E − 09	inactive	inactive	inactive	inactive
95% CI				4.0E − 009 to 1.3E − 008
P. caudatus α2-adrenergic	inactive	inactive	1.1E − 06 * p = 0.021	4.7E − 07*	inactive	4.5E − 07 ns	inactive	9.8E − 07
95% CI			4.5E − 007 to 2.4E − 006	1.7E − 007 to 1.2E − 006		1.8E − 007 to 1.0E − 006		4.3E − 007 to 2.2E − 006
P. dumerilii Tyramine-1	1.1E − 08***	2.7E − 06***	2.1E − 06	1.7E − 05	7.8E − 06	3.1E − 05	2.1E − 06	4.7E − 05
95% CI	7.6E − 009 to 1.6E − 008	1.1E − 006 to 6.1E − 006	1.0E − 006 to 4.1E − 006	1.0E − 005 to 2.8E − 005	1.5E − 006 to 3.9E − 005	9.8E − 006 to 9.9E − 005	7.0E − 007 to 6.0E − 006	1.7E − 005 to 0.00012
P. dumerilii Tyramine-2	7.0E − 09***	7.8E − 07***	5.3E − 06	1.1E − 04	3.9E − 06	4.8E − 05	5.4E − 05	6.4E − 06
95% CI	3.0E − 009 to 1.6E − 008	3.8E − 007 to 1.5E − 006	2.1E − 006 to 1.3E − 005	2.9E − 005 to 0.00038	2.1E − 006 to 7.0E − 006	8.6E − 006 to 0.00026	3.6E − 005 to 7.9E − 005	3.9E − 006 to 1.0E − 005
S. kowalevskii Tyramine-1	8.6E − 05 ns	inactive	2.9E − 04 n.s.	inactive	0.57	inactive	1.7E − 06	1.7E − 05
95% CI	2.8E − 005 to 0.00025		0.00013 to 0.00065		very wide	2.1E − 006 to 0.00017	7.1E − 007 to 3.9E − 006	7.7E − 006 to 3.7E − 005
S. kowalevskii Tyramine-2A	1.0E − 09***	8.6E − 08***	1.4E − 06	inactive	7.2E − 08	inactive	inactive	1.6E − 04
95% CI	6.6E − 010 to 1.5E − 009	4.0E − 008 to 1.8E − 007	7.4E − 007 to 2.6E − 006		1.4E − 008 to 3.5E − 007			5.4E − 008 to 0.47
S. kowalevskii Tyramine-2B	5.9E − 09***	1.6E − 06***	1.6E − 05	1.2E − 04	1.4E − 06	2.8E − 05	2.1E − 05	1.9E − 05
95% CI	2.4E − 009 to 1.4E − 008	6.5E − 007 to 3.7E − 006	6.2E − 006 to 4.0E − 005	3.6E − 005 to 0.00036	9.0E − 007 to 2.2E − 006	5.1E − 006 to 0.00015	1.1E − 005 to 3.6E − 005	1.1E − 005 to 3.0E − 005
P. dumerilii Octopamine α	1.3E − 05	2.6E − 07*	1.4E − 07 n.s.	3.5E − 06* P = 0.003	inactive	8.8E − 06	9.0E − 09	1.6E − 06
95% CI	4.2E − 006 to 4.1E − 005	8.4E − 008 to 7.7E − 007	6.7E − 008 to 3.0E − 007	1.8E − 006 to 6.7E − 006		2.5E − 006 to 3.0E − 005	4.1E − 009 to 1.9E − 008	9.7E − 007 to 2.6E − 006
S. kowalevskii Octopamine α	1.7E − 05	6.9E − 07*	1.6E − 07 * p = 0.048	5.3E − 05	2.6E − 04	1.8E − 05	7.8E − 06	2.2E − 05
95% CI	3.0E − 006 to 9.5E − 005	1.8E − 007 to 2.4E − 006	7.6E − 008 to 3.5E − 007	1.5E − 005 to 0.00018	3.4E − 006 to 0.02	7.1E − 006 to 4.7E − 005	3.1E − 006 to 1.8E − 005	1.2E − 005 to 3.6E − 005
S. kowalevskii Octopamine β	inactive	6.4E − 08***	inactive	3.5E − 06***	inactive	inactive	1.6E − 04	6.4E − 06
95% CI		4.0E − 008 to 1.0E − 007		1.4E − 006 to 8.1E − 006			1.0E − 005 to 0.0023	3.1E − 006 to 1.3E − 005

The most effective natural ligand for each receptor is shown in bold. 95% confidence intervals (CI) for the EC₅₀ (M)/IC₅₀ (M) values are given in every second line. The lowest EC₅₀ value for each receptor was compared to the next lowest one using the extra sum-of-squares F test. *P < 0.05; ***P < 0.0001; ns not significant. Significance values are shown for the compared pairs