Penitrem A

Large conductance, Ca(2+)/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 (IC(50) 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.

The effects of the fungal neurotoxin penitrem A on the GABAergic and glutamatergic systems in rat brain were evaluated. Penitrem A inhibited binding of the GABA(A)-receptor ligand [³H]TBOB to rat forebrain and cerebellar membrane preparations with IC₅₀ (half maximal inhibitory concentration) values of 11 and 9 μM, respectively. Furthermore, penitrem A caused a concentration-dependent increase of [³H]flunitrazepam and [³H]muscimol binding in rat forebrain, but not in cerebellar preparations. The stimulation of [³H]flunitrazepam binding by penitrem A was abolished by the addition of GABA. In cerebellar preparations, a different pharmacological profile was found, with penitrem A allosterically inhibiting [³H]TBOB binding by interacting with a bicuculline-sensitive site. Moreover, penitrem A inhibited the high affinity uptake of GABA and glutamate into cerebellar synaptosomes with IC₅₀ values of 20 and 47 μM, respectively. The toxin showed no effect on NMDA or AMPA glutamate receptor binding. In conclusion, our results suggest that penitrem A exerts region-specific effects in the brain, leading to positive modulation of GABA(A)-receptor function in forebrain. Conversely, penitrem A may act as a bicuculline-like convulsant in cerebellum.

Several cases of neurological disease in dogs after poisoning by food- and feed-borne Penicillium toxins in Norway during the last years have uncovered a lack of knowledge regarding the toxicity and mechanism of action of neuroactive mycotoxins. In the present study, the lowest tremor-inducing dose after single oral administration of penitrem A to mice was 0.50 mg/kg bw. The estimated half maximal effective dose (ED(50)) in respect to the visual tremor scale was 2.74 mg/kg bw. Mice receiving the maximum penitrem A dose (8 mg/kg bw) suffered severe spontaneous tremors and even convulsions. Thomitrem A and E are penitrem analogues lacking the C-16-C-18 ether linkage and possessing an olefin at C-18-C-19. Compared with penitrem A, the lowest tremor-inducing dose of thomitrem A was 16-times higher (8 mg/kg bw) and thomitrem E was found to be non-tremorgenic at the highest dose tested (16 mg/kg bw). During a recovery phase of two weeks post administration animals appeared restored and no changes in feeding and other biological processes were observed. An initial dose-related weight reduction was observed 2 days after penitrem A administration. Penitrem A was absorbed and distributed to gastrointestinal tract, liver, kidneys and brain in the mice. Elimination of penitrem A appeared to be mainly hepatic and the highest concentration levels were found 1 h post administration for all investigated organs. The relationship between liver and gastrointestinal tract concentration levels showed time-dependent linear correlation and a doubling within 1.5 h.