Figure 2.

Release of endogenous norepinephrine (NE) from guinea pig heart synaptosomes by depolarization with 3–30 mM K⁺ in the absence and presence of the selective H₃R agonist imetit (100 nM), either alone or in combination with the selective H₃R antagonist thioperamide (300 nM). Points represent mean increases in norepinephrine release above the basal level (± SEM; n = 8). The basal norepinephrine level was 1.14 ± 0.01 pmol/mg of protein. *, P < 0.05 from the corresponding control norepinephrine level by unpaired t test.