Background: Increased myocardial interstitial levels of endothelin (ET) occur during cardioplegic arrest (CA) and may contribute to contractile dysfunction. Endothelin receptor transduction involves the protein kinase-C (PKC) family comprised of multiple isoforms with diverse functions. Which PKC isoforms may be involved in ET-induced contractile dysfunction after CA remains unknown.
Methods: Shortening velocity was measured in isolated left ventricular porcine myocytes and randomized (minimum of 30 per group): normothermia (cell culture media for 2 hours at 37 degrees C); CA (2 hours in CA solution [4 degrees C, 24 mEq K+] followed by reperfusion in cell media); ET/CA (100 pM ET incubated during CA and reperfusion). These studies were carried out in the presence and absence of PKC inhibitors (500 nM) and directed against members of the classical PKC subfamily (beta I, beta II, gamma) and the novel subfamily (epsilon, eta).
Results: Cardiac arrest reduced shortening velocity by approximately 50%, which was further reduced in the presence of ET. Inhibition of either the beta II or gamma PKC isoform significantly increased shortening velocity from ET/CA as well as CA only values. In separate studies (n = 3), total beta II and phosphorylated beta II increased by over 150% with ET/CA (p < 0.05). Taken together, these results suggest that a predominant intracellular effector for the negative contractile effects mediated by ET in the context of CA is the PKC isoform beta II.
Conclusions: Targeted inhibition of specific PKC isoforms relieves the negative inotropic effects of ET after simulated CA. These findings provide important mechanistic support for the development of targeted inhibitory strategies with respect to ET signaling and myocyte contractile dysfunction in the context of CA and reperfusion.