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+], (cytosolic Ca2+ concentration) was determined in cell suspensions by means of fluorescence spectroscopy. Basal [Ca2+], was similar in platelets from BIDL 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+], that was of greater magnitude in platelets from BIDL rats than in controls. Ca2+ storage was significantly elevated in platelets from BIDL 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 BIDL 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.