Figure 1.

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 N-type Ca²⁺ channel inhibitor ω-conotoxin (100 nM). Points represent mean increases in norepinephrine release above the basal level (± SEM; n = 8). The basal norepinephrine level was 1.63 ± 0.02 pmol/mg of protein. *, P < 0.05 from the corresponding control norepinephrine level by unpaired t test.