The aim of this study was to examine the hypothesis that
delta-opioid receptor activation before
ischemia suppresses gap junction (GJ) permeability by PKC-mediated
connexin 43 (
Cx43) modulation, which contributes to
infarct size limitation afforded by the
delta-opioid receptor activation. A
delta-opioid receptor agonist, [D-Ala(2),D-Leu(5)]-
enkephalin acetate (
DADLE, 300 nM), was used in place of preconditioning (PC)
ischemia to trigger PC mechanisms in rat hearts. GJ permeability during
ischemia, which was assessed by
Lucifer yellow, was reduced by
DADLE to 47% of the control level, and this effect of
DADLE was almost abolished by a
PKC-epsilon inhibitor [
PKC-epsilon translocation inhibitory
peptide (
PKC-epsilon-TIP)] but was not affected by a PKC-delta inhibitor (
rottlerin). After
DADLE infusion,
PKC-epsilon, but not PKC-delta, was coimmunoprecipitated with
Cx43, and the level of phosphorylation of
Cx43 at a PKC-dependent site (Ser(368)) was significantly elevated during
ischemia.
DADLE reduced
infarct size after 35 min of
ischemia followed by 2 h of reperfusion by 69%, and
PKC-epsilon-TIP and
rottlerin eliminated 48% and 63%, respectively, of the
infarct size-limiting effect of
DADLE. Infusion of a GJ blocker,
heptanol, before reperfusion reduced
infarct size by 36%, and this protection was not enhanced by preischemic infusion of
rottlerin +
DADLE, which allows
PKC-epsilon activation by
DADLE. These results suggest that phosphorylation of
Cx43 by
PKC-epsilon plays a crucial role in delta-
opioid-induced suppression of GJ permeability in ischemic myocardium and that this modulation of the GJ is possibly an adjunct mechanism of
infarct size limitation afforded by preischemic
delta-opioid receptor activation.