Background Chenodeoxycholic acid (CDC) is an apolar bile salt and damages hepatocytes, whereas ursodeoxycholic acid (UDC) is a more polar bile salt and protects liver cell against toxic bile salts. We therefore inves...Background Chenodeoxycholic acid (CDC) is an apolar bile salt and damages hepatocytes, whereas ursodeoxycholic acid (UDC) is a more polar bile salt and protects liver cell against toxic bile salts. We therefore investigated the activity of membrane associated Na + K + ATPase, a coenzyme of the sodium dependent bile salt carrier. Methods Liver plasma membranes (LPM) were isolated from rat livers according to the method of Song et al (J Cell Biol 1969; 41:124). The LPM were incubated with bile salts (TUDC, UDC, TCDC, CDC) in concentrations of 0.1 2 mmol/L for 0 30 minutes at room temperature. To study reversibility of the effect of CDC, LPM were diluted with buffer 50 times of volume after incubation. The activity of membrane associated Na + K+ ATPase was determined enzymatically at 37℃ and the phospholipid (PL) release into the supernatant was measured. Results CDC and TCDC both showed a dose dependent inhibition of the enzyme activity (P<0.01 vs control). Gastroenterology, Center of Internal Medicine, University Hospital, D 60590 Frankfurt Main, Germany (You T, Guldutuna S, Bhatti S and Leuschner U)Initially TCDC induced an increase in enzyme activity at concentrations of 0.1 1 mmol/L, however, after 3 minutes activity repidly decreased to less than 30% of controls. Up to a concentration of 1 mmol/L CDC the inhibition of enzyme activity could be reversed by diluting the bile salt in the incubation medium. At a concentration of 2 mmol/L CDC activity was only partially restored and at this concentration a marked PL release into the supernatant was observed, indicating solubilization of the membranes. UDC did not decrease the enzyme activity at concentrations of 0.1 2 mmol/L. At a concentration of 2 mmol/L TUDC inhibited the Na + K + ATPase by about 20%. Solubilization of membrane PL was not observed. Conclusion CDC and TCDC inhibited Na + K + ATPase. Dilution of the bile salt with buffer reversed the inhibitory effect up to concentrations of 1 mmol/L CDC. The inhibitory effect is probably due to alteration of the plasma membrane. 2 mM CDC caused irreparable membrane damage. Physiological concentrations of UDC and TUDC did not affect membrane ATPase.展开更多
文摘Background Chenodeoxycholic acid (CDC) is an apolar bile salt and damages hepatocytes, whereas ursodeoxycholic acid (UDC) is a more polar bile salt and protects liver cell against toxic bile salts. We therefore investigated the activity of membrane associated Na + K + ATPase, a coenzyme of the sodium dependent bile salt carrier. Methods Liver plasma membranes (LPM) were isolated from rat livers according to the method of Song et al (J Cell Biol 1969; 41:124). The LPM were incubated with bile salts (TUDC, UDC, TCDC, CDC) in concentrations of 0.1 2 mmol/L for 0 30 minutes at room temperature. To study reversibility of the effect of CDC, LPM were diluted with buffer 50 times of volume after incubation. The activity of membrane associated Na + K+ ATPase was determined enzymatically at 37℃ and the phospholipid (PL) release into the supernatant was measured. Results CDC and TCDC both showed a dose dependent inhibition of the enzyme activity (P<0.01 vs control). Gastroenterology, Center of Internal Medicine, University Hospital, D 60590 Frankfurt Main, Germany (You T, Guldutuna S, Bhatti S and Leuschner U)Initially TCDC induced an increase in enzyme activity at concentrations of 0.1 1 mmol/L, however, after 3 minutes activity repidly decreased to less than 30% of controls. Up to a concentration of 1 mmol/L CDC the inhibition of enzyme activity could be reversed by diluting the bile salt in the incubation medium. At a concentration of 2 mmol/L CDC activity was only partially restored and at this concentration a marked PL release into the supernatant was observed, indicating solubilization of the membranes. UDC did not decrease the enzyme activity at concentrations of 0.1 2 mmol/L. At a concentration of 2 mmol/L TUDC inhibited the Na + K + ATPase by about 20%. Solubilization of membrane PL was not observed. Conclusion CDC and TCDC inhibited Na + K + ATPase. Dilution of the bile salt with buffer reversed the inhibitory effect up to concentrations of 1 mmol/L CDC. The inhibitory effect is probably due to alteration of the plasma membrane. 2 mM CDC caused irreparable membrane damage. Physiological concentrations of UDC and TUDC did not affect membrane ATPase.
