BmK-YA and related peptides activity at opioid receptors.

(A) Dose response curves of intracellular Ca²⁺ mobilization induced by BmK-YA in opioid receptors-expressing HEK293T cells. The EC₅₀ was 17±0.6 μM, 2.5±0.04 μM and 30±0.5 μM (mean±SE, n = 3) in μ-, δ- and κ-expressing HEK293T cells, respectively. The insert shows the inhibitory effect of naloxone on BmK-YA-induced Ca²⁺ release in δ-expressing cells (IC₅₀: 539±13 nM (mean±SE, n = 3)); BmK-YA concentration of used in this experiment was 2.5 μM. (B) Dose response curves of intracellular Ca²⁺ mobilization induced by Phe⁴-BmK-YA and His⁴-BmK-YA in μ-, δ- and κ-expressing HEK293T cells, respectively. The EC₅₀ of Phe⁴-BmK-YA was 157±3.8 nM, 60±1.1 nM, and 77±0.5 nM (mean±SE, n = 3) in μ-, δ- and κ-expressing HEK293T cells, respectively.