Paracrine Effects of Endothelial Cells in a Diabetic Mouse Model: Capacitative Calcium Entry Stimulated Thromboxane Release

Abstract

Augmented vasoconstriction contributes to arterial stiffness associated with diabetes. It has been shown that capacitative calcium entry induced by sarcoplasmic-endoplasmic reticulum calcium ATPase blocker cyclopiazonic acid (CPA) in endothelial cells stimulates production of constrictor prostaglandins, which causes contractions of vascular smooth muscle cells. The aim of the work was to study the effect of diabetes on the vasoconstrictor response induced by calcium entry into endothelial and smooth muscle cells. Force was measured in isolated aortae of diabetic ob/ob and control C57BL/6J mice under isometric conditions. Contractions caused by 10 μmol/l CPA in diabetic mouse aortae featured higher amplitudes and longer durations in comparison with nondiabetic aortae. These contractions were abolished by a COX inhibitor indomethacin (10 μmol/l) or a specific thromboxane A2 receptor blocker SQ 29548 (1 μmol/l) and were not observed in denuded aortae. The contractions were sensitive to extracellular Ca²⁺ and store-operated channel blockers. All together this suggests that vasoconstriction was caused by thromboxane A2 synthesis in endothelial cells induced by Ca²⁺ entry through store-operated channels. Higher concentrations of CPA (30 μmol/l) or thapsigargin (1 μmol/l) elicited indomethacin-resistant tonic contractions of aortae with 2-fold amplitude in diabetic mice compared to their nondiabetic littermates, which were sensitive to store-operated channel blockers, but not to indomethacin, SQ 29548, or denudation. In conclusions, increases in intracellular Ca²⁺ cause augmented vasoconstriction in diabetic vasculature through endothelial synthesis of contractile prostaglandins. In addition capacitative Ca²⁺ entry is enhanced in diabetic vascular smooth muscle. These mechanisms indicate possible targets for clinical applications.

Key words

ob/ob mice - vasoconstriction - mouse aorta - sarcoplasmic/endoplasmic reticulum ATPase - thromboxane A2 receptor

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