Endothelin-1 and PKC induce positive inotropy without affecting pHi in ventricular myocytes.
Exp Biol Med (Maywood)
; 231(6): 865-70, 2006 Jun.
Article
em En
| MEDLINE
| ID: mdl-16741014
ABSTRACT
It has been proposed that intracellular alkalinization underlies the enhanced contractility of ventricular myocytes exposed to endothelin (ET)-1. The effects of ET-1 on the contractility and intracellular pH (pH(i)) were examined here in cultured adult rat ventricular myocytes by employing the pH-sensitive fluorescent dye SNARF-1. Variable pH(i) changes were observed on ET-1 stimulation. Most myocytes (n = 20 of 32) did not alkalinize, but showed an approximate 60% increase in twitch amplitude in response to ET-1. In the remaining myocytes (12 of 32), ET-1 induced an increase in pH(i) by 0.05 +/- 0.02 pH units with a similar approximate 60% increase in twitch amplitude. Therefore, there was no strong correlation between ET-1-mediated positive inotropy (enhanced contractility) and intracellular alkalinization. To determine whether ET-1 contractile and pH(i) responses were mediated by protein kinase C (PKC), yellow fluorescent protein (YFP)-fused dominant negative (dn) PKC constructs were used as isoform specific inhibitors. In dn-PKC-epsilon-YFP-expressing myocytes, the ET-1-mediated positive inotropic response was greatly diminished to 13 +/- 15%, but alkalinization was still observed. Expression of dn-PKC-delta-YFP also did not block alkalinization, but in this case the positive inotropic response was still observed. In a previous study, we showed that expression of PKC-delta and PKC-epsilon caused a strong positive inotropy on stimulation with phorbol 12,13-dibutyrate (PDBu). Using this system, PDBu failed to affect pH(i) in the majority of PKC expressing myocytes despite increases in twitch amplitudes of >60%. Overall, the poor correlation of positive inotropic responses and alkalinization was observed for ET-1 with and without dn-PKC constructs and for PDBu with and without wild-type PKC constructs. These results suggest that ET-1 produces positive inotropy via PKC-epsilon by mechanisms other than intracellular alkalinization.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Proteína Quinase C
/
Endotelina-1
/
Miócitos Cardíacos
/
Ventrículos do Coração
Limite:
Animals
Idioma:
En
Ano de publicação:
2006
Tipo de documento:
Article