Characterisation of explanted endothelial cells from mouse aorta: Electrophysiology and Ca²⁺ signalling

We describe here the isolation and primary culture of endothelial cells from mouse aorta ('primary explant technique'). These cells provide an excellent model for functional studies in transgenic mice. The primary explant method delivers cells that grow out from small pieces of mouse aorta placed on Matrigel enriched with endothelial growth factors. Cells can be studied on the Matrigel after removing the pieces of aorta or after passages by using dispase and reseeding the cells on gelatine-coated cover-slips. Cells on Matrigel or from the first and second passages were characterised using the combined patch-clamp and fura-2 fluorescence methods. Cells had a mean membrane resting potential of-19 ± 3 mV (n=21), a membrane capacitance of 49 ± 5 pF (n=37) and a resting cytosolic free [Ca²⁺] ([Ca²⁺](i)) of 103 ± 8 nM (n=30). Adenosine 5'-triphosphate (ATP), acetylcholine and bradykinin, but not histamine, induced fast release of intracellular Ca²⁺ followed by a sustained rise in [Ca²⁺](i). Oscillations in [Ca²⁺](i) were observed at lower agonist concentrations. In nearly all cells (93%, n=30), these agonists activated charybdotoxin-sensitive, Ca²⁺-activated K⁺ channels and induced hyperpolarisation. In 84% of the cells (n=32), an increase in [Ca²⁺](i) also activated strongly outwards-rectifying Cl- channels. These activated slowly at positive potentials and inactivated rapidly at negative potentials. Increasing [Ca²⁺](i) to 1 μM activated a non-selective cation channel in 86% of the cells (n=28). Each tested cell responded to a challenge with hypotonic solution by activating a Cl- current that was modestly outwards rectifying and inactivated at positive potentials. This current is similar to the well-described swelling-activated current through volume-regulated anion channels (VRAC) in endothelial cells. However, its activation is slower, its inactivation faster and the current density lower than in cultured endothelial cells. It is concluded that the primary explant technique provides a reliable cell model for studying mouse vascular endothelial cell function.