Resistance to store depletion-induced endothelial injury in rat lung after chronic heart failure

Rationale: In chronic heart failure, the lung endothelial permeability response to angiotensin II or thapsigargin-induced store depletion is ablated, although the mechanisms are not understood. Objectives: To determine whether the ablated permeability response to store depletion during heart failure was due to impaired expression of store operated Ca(2+) channels in lung endothelium. Methods: Heart failure was induced by aortocaval fistula in rats. Permeability was measured in isolated lungs using the filtration coefficient and a low Ca(2+)/Ca(2+) add-back strategy to identify the component of the permeability response dependent on Ca(2+) entry. Main Results: In fistulas, right ventricular mass and left ventricular end diastolic pressure were increased and left ventricular shortening fraction decreased compared with shams. Thapsigargin-induced store depletion increased lung endothelial permeability in shams, but not in fistulas. Permeability increased in both groups after the Ca(2+) ionophore A23187 or 14,15-epoxyeicosatrienoic acid, independent of store depletion. A diacylglycerol analog had no impact on permeability. Increased distance between the endoplasmic reticulum and the plasmalemmal membrane was ruled out as a mechanism for the loss of the permeability response to store depletion. Endothelial expression of the endoplasmic reticulum Ca(2+) ATPase was not altered in fistulas compared with shams, whereas the store-operated canonical transient receptor potential channels 1, 3, and 4 were downregulated in extraalveolar vessel endothelium. Conclusions: We conclude that the adaptive mechanism limiting store depletion-induced endothelial lung injury in the aortocaval model of heart failure involves downregulation of store-operated Ca(2+) channels.