Penitrem A as a Tool for Understanding the Role of Large Conductance Ca²⁺/Voltage-Sensitive K⁺Channels in Vascular Function

Abstract

Large conductance, Ca 2ϩ /voltage-sensitive K ϩ 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 ␣ or ␣ ϩ ␤1 were blocked Ͼ95% by penitrem A (IC 50 6.4 versus 64.4 nM; p Ͻ 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 ϩ currents were equivalent to iberiotoxin in canine coronary smooth muscle cells. As for specificity, penitrem A had no effect on native delayed rectifier K ϩ currents, cloned voltage-dependent Kv1.5 channels, or native ATP-dependent K ATP current. Penitrem A enhanced the sensitivity to K ϩ -induced contraction in canine coronary arteries by 23 Ϯ 5% (p Ͻ 0.05) and increased the blood pressure response to phenylephrine in anesthetized mice by 36 Ϯ 11% (p Ͻ 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.

Inhibition of Myogenic Tone in Rat Cremaster and Cerebral Arteries by SKA-31, an Activator of Endothelial KCa2.3 and KCa3.1 Channels

“…To further establish the selective activation of KCa2.3 and KCa3.1 channels by SKA-31 in myogenically active vessels, cremaster and middle cerebral arteries were treated with 2 μM penitrem-A, a highly selective pharmacologic blocker of large conductance, Ca 2+ -activated K + (BK Ca ) channels 22 . As shown in Figure 5, the extent of inhibition of myogenic tone by SKA-31 was unaltered in the presence of penitrem-A and we also observed no effect of this treatment on the vasodilatory action of the K ATP channel activator pinacidil.…”

Central role of the BK channel in urinary bladder smooth muscle physiology and pathophysiology

“…Another advantage of paxilline vs. iberiotoxin and charybdotoxin is that paxilline is a small hydrophobic molecule that can easily cross the cell plasma membrane and block the BK channels from inside, while recorded in the cell-attached patch-clamp configuration. The mycotoxin penitrem A is another BK channel inhibitor with inhibitory properties similar to those of paxilline (12,72,99). BK channels are also inhibited nonselectively by tetraethylammonium, but with low affinity (21,53,117).…”

BK Channels Mediate Synaptic Plasticity Underlying Habituation in Rats

“…Both paxilline and penitrem A are very potent blocker of BK channels with only some minor effects on the pH-sensitive slo-3 at higher doses (Zhang et al, 2006), and no effects on delayed rectifier K(ϩ) currents, cloned voltagedependent Kv1.5 channels, or native ATP-dependent K(ATP) current (Asano et al, 2012). Likewise, BMS-204352 has been shown to be highly selective (Hewawasam et al, 2002) while having a minor effect on L-type calcium channels (Son et al, 2011).…”