ALTERATIONS IN VASOPRESSIN AND ANGIOTENSIN-II RECEPTORS AND RESPONSES DURING CULTURE OF RAT-LIVER CELLS

Vasopressin and angiotensin II binding and responses were studied in hepatocytes in primary culture for 4 h and 24 h. After 24 h of culture, angiotensin II was completely ineffective in elevating cytosolic [Ca2+], whereas the maximum [Ca2+] response to vasopressin was decreased by 66% and the sensitivity to the hormone was decreased approx. 20-fold compared with values after 4 h of culture. The dissociation constant (K(D)) for vasopressin binding to the cells was not significantly changed during 24 h of culture, but the B(max) was decreased by 63% compared with 4 h of culture. There was also no change in the K(D) for angiotensin II binding from 4 h to 24 h, but the B(max) was decreased by 90%. After 24 h of culture, there was no change in the plasma membrane concentration of phosphatidylinositol 4,5-bisphosphate or in angiotensin II and the response to 100 nM vasopressin was reduced by 66% compared with that at 4 h. The effect of guanosine 5'-(3-O-thiol) triphosphate on the polyphosphoinositide phospholipase C activity of liver cell plasma membranes was also measured. There was no decrease in the degree of stimulation of the phospholipase by this nucleotide after 24 h of culture. It is concluded that the loss of vasopressin and angiotensin II responses in cultured liver cells is due in part to changes in receptors and also in their coupling to a guanine nucleotide binding protein.