Dataset Information

Effects of vasopressin and La3+ on plasma-membrane Ca2+ inflow and Ca2+ disposition in isolated hepatocytes. Evidence that vasopressin inhibits Ca2+ disposition.

ABSTRACT: Vasopressin caused a 40% inhibition of 45Ca uptake after the addition of 0.1 mM-45Ca2+ to Ca2+-deprived hepatocytes. At 1.3 mM-45Ca2+, vasopressin and ionophore A23187 each caused a 10% inhibition of 45Ca2+ uptake, whereas La3+ increased the rate of 45Ca2+ uptake by Ca2+-deprived cells. Under steady-state conditions at 1.3 mM extracellular Ca2+ (Ca2+o), vasopressin and La3+ each increased the rate of 45Ca2+ exchange. The concentrations of vasopressin that gave half-maximal stimulation of 45Ca2+ exchange and glycogen phosphorylase activity were similar. At 0.1 mM-Ca2+o, La3+ increased, but vasopressin did not alter, the rate of 45Ca2+ exchange. The results of experiments performed with EGTA or A23187 or by subcellular fractionation indicate that the Ca2+ taken up by hepatocytes in the presence of La3+ is located within the cell. The addition of 1.3 mM-Ca2+o to Ca2+-deprived cells caused increases of approx. 50% in the concentration of free Ca2+ in the cytoplasm [( Ca2+]i) and in glycogen phosphorylase activity. Much larger increases in these parameters were observed in the presence of vasopressin or ionophore A23187. In contrast with vasopressin, La3+ did not cause a detectable increase in glycogen phosphorylase activity or in [Ca2+]i. It is concluded that an increase in plasma membrane Ca2+ inflow does not by itself increase [Ca2+]i, and hence that the ability of vasopressin to maintain increased [Ca2+]i over a period of time is dependent on inhibition of the intracellular removal of Ca2+.

SUBMITTER: Hughes BP

PROVIDER: S-EPMC1147206 | biostudies-other | 1986 Sep

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:The roles of heterotrimeric GTP-binding regulatory proteins (G-proteins) and inositol polyphosphates in the mechanism by which vasopressin stimulates Ca2+ inflow in hepatocytes were investigated by using single cells loaded with fura2 by microinjection. Vasopressin-stimulated Ca2+ inflow was mimicked by microinjection of guanosine 5'-[gamma-thio]triphosphate (GTP[S]) or guanosine 5'-[beta gamma-imido]triphosphate to the cells, but not adenosine 5'-[gamma-thio]triphosphate (ATP[S]) or guanosine 5'-[beta-thio]diphosphate (GDP[S]). Extracellular Gd3+ (5 microM) inhibited both vasopressin- and GTP[S]-stimulated Ca2+ inflow. GDP[S], but not GMP, administered to hepatocytes by microinjection, completely inhibited vasopressin-stimulated Ca2+ inflow and partially inhibited vasopressin-induced release of Ca2+ from intracellular stores. The microinjection of pertussis toxin had no effect either on the release of Ca2+ from intracellular stores or on Ca2+ inflow induced by vasopressin, but completely inhibited changes in these processes induced by epidermal growth factor (EGF). Hepatocytes isolated from rats treated with pertussis toxin for 24 h exhibited no vasopressin- or GTP[S]-stimulated Ca2+ inflow, whereas the vasopressin-stimulated release of Ca2+ from intracellular stores was similar to that observed for control cells. Heparin or ATP[S] inhibited, or delayed the onset of, both vasopressin-induced release of Ca2+ from intracellular stores and vasopressin-stimulated Ca2+ inflow. Vasopressin-induced oscillations in intracellular [Ca2+] were observed in some heparin-treated cells. It is concluded that the stimulation by vasopressin of Ca2+ inflow to hepatocytes requires inositol 1,4,5-trisphosphate (InsP3) and, by implication, the pertussis-toxin-insensitive G-protein required for the activation of phospholipase C beta [Taylor, Chae, Rhee and Exton (1991) Nature (London) 350, 516-518], and another G-protein which is slowly ADP-ribosylated by pertussis toxin and acts between InsP3 and the putative plasma-membrane Ca2+ channel. EGF-stimulated Ca2+ inflow involves at least one G-protein which is rapidly ADP-ribosylated and is most likely required for InsP3 formation.

Dataset Information

Effects of vasopressin and La3+ on plasma-membrane Ca2+ inflow and Ca2+ disposition in isolated hepatocytes. Evidence that vasopressin inhibits Ca2+ disposition.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets