Browsing by Author "Kushmerick, Christopher"

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    Antiarrhythmogenic effects of a neurotoxin from the spider Phoneutria nigriventer.
    (2011) Almeida, Alvair Pinto de; Andrade, Alexandre Barbosa; Ferreira, Anderson José; Pires, Andrea Cristina Gomes; Damasceno, Dênis Derly; Alves, Márcia Netto Magalhães; Gomes, Enéas Ricardo de Morais; Kushmerick, Christopher; Lima, Ricardo de Freitas; Prado, Marco Antônio Maximo; Prado, Vânia Ferreira; Richardson, Michael; Cordeiro, Marta do Nascimento; Guatimosim, Silvia; Gomez, Marcus Vinicius
    In this study, we evaluated the effects of PhKv, a 4584 Da peptide isolated from the spider Phoneutria nigriventer venom, in the isolated rat heart and in isolated ventricular myocytes. Ventricular arrhythmias were induced by occlusion of the left anterior descending coronary artery for 15 min followed by 30 min of reperfusion. Administration of native PhKv (240 nM) 1 min before or after reperfusion markedly reduced the duration of arrhythmias. This effect was blocked by atropine, thereby indicating the participation of muscarinic receptors in the antiarrhythmogenic effect of PhKv. Notably, recombinant PhKv (240 nM) was also efficient to attenuate the arrhythmias (3.8 0.9 vs. 8.0 1.2 arbitrary units in control group). Furthermore, PhKv induced a significant reduction in heart rate. This bradycardia was partially blunted by atropine and potentiated by pyridostigmine. To further evaluate the participation of acetylcholine on the PhKv effects, we examined the release of this neurotransmitter from neuromuscular junctions. It was found that Phkv (200 nM) significantly increased the release of acetylcholine in this preparation. Moreover, PhKv (250 nM) did not cause any significant change in action potential or Ca2þ transient parameters in isolated cardiomyocytes. Altogether, these findings show an important acetylcholine-mediated antiarrhythmogenic effect of the spider PhKv toxin in isolated hearts.
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    Phoneutria toxin PnTx3-5 inhibits TRPV1 channel with antinociceptive action in an orofacial pain model.
    (2020) Pereira, Elizete Maria Rita; Souza, Jéssica Mabelle; Carobin, Natália Virtude; Silva, Juliana Figueira da; Astoni, Duana Carvalho dos Santos; Silva Júnior, Cláudio Antônio da; Binda, Nancy Scardua; Borges, Marcia Helena; Nagem, Ronaldo Alves Pinto; Kushmerick, Christopher; Ferreira, Juliano; Castro Junior, Célio José de; Ribeiro, Fabiola Mara; Gomez, Marcus Vinicius
    Capsaicin, an agonist of TRPV1, evokes intracellular [Ca2+] transients and glutamate release from perfused trigeminal ganglion. The spider toxin PnTx3-5, native or recombinant is more potent than the selective TRPV1 blocker SB-366791 with IC50 of 47 ± 0.18 nM, 45 ± 1.18 nM and 390 ± 5.1 nM in the same experimental conditions. PnTx3-5 is thus more potent than the selective TRPV1 blocker SB-366791. PnTx3-5 (40 nM) and SB-366791 (3 μM) also inhibited the capsaicin-induced increase in intracellular Ca2+ in HEK293 cells transfected with TRPV1 by 75 ± 16% and 84 ± 3.2%, respectively. In HEK293 cells transfected with TRPA1, cinnamaldehyde (30 μM) generated an increase in intracellular Ca2+ that was blocked by the TRPA1 antagonist HC-030031 (10 μM, 89% inhibition), but not by PnTx3-5 (40 nM), indicating selectivity of the toxin for TRPV1. In whole-cell patch-clamp experiments on HEK293 cells transfected with TRPV1, capsaicin (10 μM) generated inward currents that were blocked by SB-366791 and by both native and recombinant PnTx3-5 by 47 ± 1.4%; 54 ± 7.8% and 56 ± 9.0%, respectively. Intradermal injection of capsaicin into the rat left vibrissa induced nociceptive behavior that was blocked by pre-injection with either SB-366791 (3 nmol/site i.d., 83.3 ± 7.2% inhibition) or PnTx3-5 (100 fmol/site, 89 ± 8.4% inhibition). We conclude that both native and recombinant PnTx3-5 are potent TRPV1 receptor antagonists with antinociceptive action on pain behavior evoked by capsaicin.