Penitrem A as a tool for understanding the role of large conductance Ca²⁺/ voltage-sensitive K⁺ channels in vascular function

Large conductance, Ca²⁺/voltage-sensitive K⁺ channels (BK channels) are well characterized, but their physiological roles, often determined through pharmacological manipulation, are less clear. Iberiotoxin is considered the "gold standard" antagonist, but cost and membrane-impermeability limit its usefulness. Economical and membrane-permeable alternatives could facilitate the study of BK channels. Thus, we characterized the effect of penitrem A, a tremorigenic mycotoxin, on BK channels and demonstrate its utility for studying vascular function in vitro and in vivo. Whole-cell currents from human embryonic kidney 293 cells transfected with hSlo α or α + β1 were blocked >95% by penitrem A (IC₅₀ 6.4 versus 64.4 nM; p < 0.05). Furthermore, penitrem A inhibited BK channels in inside-out and cell-attached patches, whereas iberiotoxin could not. Inhibitory effects of penitrem A on whole-cell K⁺ currents were equivalent to iberiotoxin in canine coronary smooth muscle cells. As for specificity, penitrem A had no effect on native delayed rectifier K⁺ currents, cloned voltage-dependent Kv1.5 channels, or native ATP-dependent K_ATP current. Penitrem A enhanced the sensitivity to K ⁺-induced contraction in canine coronary arteries by 23 ± 5% (p < 0.05) and increased the blood pressure response to phenylephrine in anesthetized mice by 36 ± 11% (p < 0.05). Our data indicate that penitrem A is a useful tool for studying the role of BK channels in vascular function and is practical for cell and tissue (in vitro) studies as well as anesthetized animal (in vivo) experiments.