Altered calcium signalling in platelets from bile-duct-ligated rats

In the present study, we have analysed the mechanisms of Ca²⁺ entry and release in platelets obtained from BDL (bile-duct-ligated) rats, 11–13 days and 4 weeks after surgery. Platelets were washed and loaded with fura-2, and [Ca²⁺]_i (cytosolic Ca²⁺ concentration) was determined in cell suspensions by means of fluorescence spectroscopy. Basal [Ca²⁺]_i was similar in platelets from BDL rats compared with those from their respective controls, both in the absence and presence of extracellular Ca²⁺. Platelet stimulation with thrombin in the absence and presence of extracellular Ca²⁺ induced a rapid rise in [Ca²⁺]_i that was of greater magnitude in platelets from BDL rats than in controls. Ca²⁺ storage was significantly elevated in platelets from BDL rats, as well as the activity of SERCA (sarcoplasmic/endoplasmic-reticulum Ca²⁺-ATPase). Capacitative Ca²⁺ entry, as evaluated by inhibition of SERCA with thapsigargin, was also altered in platelets from BDL rats, having lower rates of Ca²⁺ entry. In conclusion, chronic BDL alters intracellular Ca²⁺ homoeostasis in platelets, such that an enhanced Ca²⁺ release is evoked by thrombin, which may be due to an increased amount of Ca²⁺ stored in the intracellular organelles and secondary to an enhanced activity of SERCA. These alterations are already evident before cirrhosis has completely developed and occurs during the cholestasis phase.