3.2 U PTAKE DI CALCIO - Attività anti-ischemica della Naringenina e coinvolgimento di canali de

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Il potenziale di membrana dei mitocondri cardiaci utilizzati negli

esperimenti è stato misurato per via indiretta (uptake di TPP+_{) ed è ri-}

sultato pari a -180 mV.

Questo valore, corrispondendo esattamente a quello fisiologico, ci ha dato conferma della validità del metodo di isolamento.

La Naringenina (Fig.11) ha portato ad una depolarizzazione concentrazione-dipendente della membrana interna dei mitocondri cardiaci, che si attesta ad un livello pari a 22±4 mV per la concentrazione 100 µM del flavonoide.

Sebbene una depolarizzazione dell’ordine dei 20 mV potrebbe sem- brare modesta, precedenti studi sperimentali hanno dimostrato che una depolarizzazione di tale entità è comunque sufficiente a garantire un

significativo effetto sui movimenti del Ca2+ _{ed una conseguente atti-}

vità cardioprotettiva (Calderone et al., 2010).

Fig. 11 - [*] La significatività è calcolata sull’ultima concentrazione di !aringenina (100 µM).

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Allo scopo di verificare che tale depolarizzazione fosse legata al-

l’attivazione di flussi di K+_{, l’effetto depolarizzante della Naringe-}

nina è stato valutato in un buffer al mannitolo, privo cioè dello ione K+_.

Se l’attività depolarizzante della Naringenina fosse stata legata al-

l’apertura di canali diversi da quelli del K+ _{, l’utilizzo del buffer al}

mannitolo non avrebbe influenzato minimamente l’entità della depolarizzazione che, dunque, sarebbe stata uguale al controllo.

Invece, la somministrazione della Naringenina in assenza di K+_nel-

l’ambiente extramitocondriale ha determinato un effetto depolarizzante significativamente inferiore al controllo (10±4 mV con Naringenina 100 µM) confermando, così, che i canali ionici mitocon-

driali coinvolti sono quelli al K+_{. Infine, per avere la certezza che fra}

tutti i canali del K+_{espressi a livello mitocondriale quelli coinvolti nel}

meccanismo di protezione cardiaca fossero canali BK, la depolarizzazione del potenziale di membrana indotta dalla Naringenina è stata misurata in presenza di due noti BK-bloccanti selettivi, l’IbTx e la Pax, alle concentrazioni rispettivamente di 100 nM e 10 µM.

I due BK-bloccanti hanno antagonizzato pressoché totalmente la risposta depolarizzante della Naringenina, indicando il coinvolgimento dei canali BK mitocondriali.

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3.3 - C

O!CLUSIO!I

L’indagine sperimentale eseguita ci ha permesso di verificare l’ef- ficacia anti-ischemica del flavonoide Naringenina e di correlare tale effetto al coinvolgimento di canali BK espressi a livello mitocondriale.

I risultati mostrano, dunque, un interessante meccanismo farma- codinamico della Naringenina, responsabile dell’effetto cardiopro- tettivo in modo sinergico, se non addirittura predominante, rispetto alle proprietà antiossidanti già ben note per i flavonoidi del genere Citrus.

Tali conclusioni concordano perfettamente con i risultati ottenuti da precedenti studi sperimentali (Moonkyu et al., 2007).

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