The gap junction uncoupler heptanol abrogates infarct size reduction with preconditioning in mouse hearts.
BACKGROUND
Emerging evidence suggests that gap junction-mediated intercellular transmission of ions, metabolites and/or second messengers may serve as important determinants of myocyte viability. Our aim was to determine, using isolated buffer-perfused mouse hearts, whether the cardioprotection achieved with ischemic preconditioning (PC) is due in part to: (i) disruption of cell-cell coupling (manifest as a loss in the primary gap junction protein, connexin 43 [Cx43]) and resultant impaired transmission of a 'death' messenger, or conversely, (ii) transfer of a humoral 'survival' factor via existing gap junctions.


METHODS
To explore the first possibility, we employed immunostaining to visualize and quantify Cx43 in hearts subjected to 212 min of PC ischemia or a matched control period. To test the converse corollary, we assessed the effect of heptanol-an agent well recognized to rapidly and reversibly uncouple gap junctions--on the reduction of infarct size (delineated by tetrazolium staining) achieved with PC.


RESULTS
We found no evidence of a deficit in Cx43 immunoreactive signal in response to the PC stimulus. Area of necrosis (AN) was, as expected, reduced in hearts that received PC ischemia vs. controls (31+/-3% vs. 40+/-3% of the left ventricle [LV]; P<.01). However, treatment with heptanol rendered PC ineffective in eliciting protection (AN/LV: 42+/-1%).


CONCLUSIONS
Our results suggest that gap junction-mediated transfer of an as-yet unknown 'survival' factor-rather than disrupted transfer of a 'death messenger'-may play a role in the increased resistance to infarction conferred by antecedent PC ischemia in mouse heart.