Altered calcium regulation in freshly isolated aortic smooth muscle cells from bile duct-ligated rats: Role of nitric oxide

In the present study we have analyzed the mechanisms of calcium entry and mobilization in smooth muscle cells (SMCs) freshly isolated from the abdominal aorta of rats with bile duct ligation (BDL). The SMCs were obtained in the day of the experiment after collagenase digestion and loaded with fura-2. The intracellular calcium levels ([Ca]_i) were determined in individual cells by fluorescence microscopy. Baseline [Ca]_i was slightly but significantly lower in SMCs from BDL rats (70.14 ± 2.02 nM, n = 51) than in controls (80.77 ± 3.52, n = 44). The application of the purinergic agonists ATP and UTP induced a fast calcium peak and a slow return to baseline. But the calcium responses were significantly smaller in the cells from the BDL rats. Also, the area under the curve (AUC) of the calcium responses elicited by the agonists was always lower in the SMCs from BDL rats as compared to the controls. Similar results were obtained with UTP, but the calcium response of the SMCs from the BDL rats was even lower than that observed with ATP. In experiments performed in the absence of extracellular calcium, both agonists also elevated [Ca]_i, although the responses were much smaller than those obtained in the presence of calcium. Again, the peak and AUC responses of the SMCs from BDL rats were significantly lower than those of the controls. Incubation with NNA, a non-specific nitric oxide synthase (NOS) inhibitor, or with NIL, an inducible NOS inhibitor (iNOS), potentiated and normalized the calcium responses of the SMCs obtained from BDL rats. These data indicate that, in SMCs from bile duct-ligated rats, both the entry of calcium and the mobilization from internal stores is defective in response to purinergic agonists. NO, of an inducible origin, is involved in this altered calcium regulation.