Cell culture as models for studying neural functions

Ammonium-induced calcium mobilization in 1321N1 astrocytoma cells

High blood levels of ammonium/ammonia (NH(4)(+)/NH(3)) are associated with severe neurotoxicity as observed in hepatic encephalopathy (HE). Astrocytes are the main targets of ammonium toxicity, while neuronal cells are less vulnerable. In the present study, an astrocytoma cell line 1321N1 and a neuroblastoma glioma hybrid cell line NG108-15 were used as model systems for astrocytes and neuronal cells, respectively. Ammonium salts evoked a transient increase in intracellular calcium concentrations ([Ca(2+)](i)) in astrocytoma (EC(50)=6.38 mM), but not in NG108-15 cells. The ammonium-induced increase in [Ca(2+)](i) was due to an intracellular effect of NH(4)(+)/NH(3) and was independent of extracellular calcium. Acetate completely inhibited the ammonium effect. Ammonium potently reduced calcium signaling by G(q) protein-coupled receptors (H(1) and M3) expressed on the cells. Ammonium (5 mM) also significantly inhibited the proliferation of 1321N1 astrocytoma cells. While mRNA for the mammalian ammonium transporters RhBG and RhCG could not be detected in 1321N1 astrocytoma cells, both transporters were expressed in NG108-15 cells. RhBG and RhBC in brain may promote the excretion of NH(3)/NH(4)(+) from neuronal cells. Cellular uptake of NH(4)(+)/NH(3) was mainly by passive diffusion of NH(3). Human 1321N1 astrocytoma cells appear to be an excellent, easily accessible human model for studying HE, which can substitute animal studies, while NG108-15 cells may be useful for investigating the role of the recently discovered Rhesus family type ammonium transporters in neuronal cells. Our findings may contribute to the understanding of pathologic ammonium effects in different brain cells, and to the treatment of hyperammonemia.

The role of bradykinin in the etiology of vasogenic brain edema and perilesional brain dysfunction

The feline infusion model of brain edema was used to evaluate the role of bradykinin in the etiology and pathophysiology of vasogenic brain edema. Bradykinin (3 or 90 ug in 600 microL saline) did not alter normocapnic regional cerebral blood flow (rCBF) nor induce specific changes in either the somatosensory (SEP) or motor (MEP) evoked potentials. The mean increases in ICP (from 4.5 to 16.1 mmHg) and peri-infusion white matter water content (from 69.4 to 79.8 ml/100 g tissue), mean decrease in lumped craniospinal compliance (from 0.040 to 0.014 ml/mmHg) and local histological changes were all similar to those after 600 microL saline infusion. The interstitial bradykinin infusion caused focal blood-brain-barrier (BBB) opening to Evans Blue dye and was chemotaxic for granulocytes. After the infusion there was a global loss of rCBF CO2 reactivity but there was no ischemia at normocapnia. These results show that bradykinin in brain edema fluid, at concentrations greater than those found in neuropathological conditions, can open the BBB of normal cerebral parenchymal capillaries and cause vascular dysregulation. In neuropathological conditions bradykinin may therefore potentiate formation of vasogenic brain edema but does not contribute to perilesional brain dysfunction.

Acetylcholine synthesis and secretion by LA-N-2 human neuroblastoma cells

We have investigated the rates of acetylcholine (ACh) synthesis and release in LA-N-2 cells in order to characterize them as a potential model of cholinergic neurons. When grown in a serum-containing medium the cells extend few neurites. In the absence of serum most cells develop processes. ACh content of the cells (determined by a radioenzymatic assay) varies with extracellular choline concentration in a saturable fashion, reaching a maximum of approximately 25 nmol/mg protein. Radiolabeled choline is taken up by the cell and converted to ACh or phosphocholine, as determined by purification from cell extracts by HPLC, in a saturable manner which is described by a single rectangular hyperbola. Hemicholinium-3 (100 microM) inhibits this uptake. The cells release ACh spontaneously and this release is enhanced upon depolarization with potassium or veratridine (the latter effect is blocked by tetrodotoxin). The data demonstrate that LA-N-2 cells exhibit some properties similar to cholinergic neurons and may therefore be useful for studies of ACh synthesis and release.