NCB-20 Cell Research Articles

DESENSITIZATION OF PROSTACYCLIN RECEPTORS IN A NEURONAL HYBRID CELL LINE

1 Prostacyclin and its stable analogue, carbacyclin, bind competitively to a single population of receptors, and activate adenylate cyclase of the NCB-20 neuronal somatic cell hybrid (Kact = 40.1 nM and 96.1 nM respectively). 2 Culture of NCB-20 cells in the presence of 1 microM carbacyclin for 4 to 16 h results in a progressive decrease in the prostacyclin-dependent activation of adenylate cyclase in cell homogenates with an increase at 16 h of the Kact from 64.1 nM to 174.0 nM and decrease in the maximum adenylate cyclase activation from 41.2 to 15.1 pmol cyclic AMP min-1 mg-1 protein. 3 The prediction that the apparent decrease in affinity in the prostacyclin-dependent activation of adenylate cyclase was secondary to a reduction in receptor numbers was tested directly by measuring binding of [3H]-prostacyclin to membranes of cells exposed to carbacyclin for 16 h. This showed an actual decrease in affinity of the prostacyclin-receptor interaction, as well as a decrease in the total receptor numbers. Thus prolonged exposure of NCB-20 cells to carbacyclin caused reductions in both receptor numbers and affinity, reflected by measurements both of binding and adenylate cyclase activation.

The binding of [3H]-prostacyclin to membranes of a neuronal somatic hybrid.

1 [3H]-prostacyclin bound to a washed membrane preparation of the NCB-20 neuronal hybrid cell line. 2 Kinetic analysis of [3H]-prostacyclin binding suggested a simple, non-cooperative bimolecular interaction between the ligand and a single receptor population. The equilibrium dissociation constant was 16.6 nM, and binding at a saturating [3H]-prostacyclin concentration enabled the receptor density of 2.57 x 10(5) receptor molecules per cell to be calculated. 3 At 20 degrees C the rate constant for the forward reaction (K+1) was 2.26 x 10(5) M-1 S-1, and the rate constant for the dissociation of the ligand-receptor complex (k-1) was 3.85 x 10(-3) S-1. Thus the dissociation constant (k-1/k+1) was 17.0 nM. 4 Prostaglandin E1 and prostacyclin compete for a single receptor in these cells, and comparison of other prostaglandins as inhibitors of [3H]-prostacyclin binding revealed some of the structural requirements for high-affinity occupation of prostacyclin receptors.

Expression of A and B types of monoamine oxidase in neuroblastoma hybrid cells

Monoamine oxidase (MAO) activity towards kynuramine as substrate was measured in 6 hybrid cells derived by fusion of neuroblastoma and glioma, liver or brain cells, and was compared with that of parental or non-parental clones. Activities varied from the lowest level of less than 0.15 pmol/min/mg protein in a neuroblastoma clone NB2A to the highest level of 127 pmol/min/mg protein in NCB20 mouse neuroblastoma × Chinese hamster embryo brain hybrid cells. The relative proportions of A and B types of MAO activities were determined in homogenates of each cell line by inhibition curves with clorgyline and deprenyl. Although the A type activity was found in all cell lines measured, MAO A was predominant in 9 clones, except for NCB20 hybrid cells, N4G-B-a neuroblastoma × glioma hybrid cells, and G8-1 myoblast. The ratio of type A/type B activity in NCB20, N4G-B-a and G8-1 cells was 20/80, 75/25 and 95/5, respectively. The results suggest that NCB20 cells are highly enriched in MAO type B, and that the NCB20 cell is an excellent model for studying the type B activity found in the brain in vivo.

Prostacyclin-dependent activation of adenylate cyclase in a neuronal somatic cell hybrid: prostanoid structure-activity relationships.

1 Prostacyclin activates adenylate cyclase of the NCB-20 neuronal hybrid cell line. 2 There is a guanosine 5'-triphosphate requirement for the activation of adenylate cyclase by 5,6 beta-dihydroprostacyclin (a stable analogue of prostacyclin). 3 Steady-state kinetic analysis of the activation of adenylate cyclase by 5,6 beta-dihydroprostacyclin suggests a simple non-cooperative bimolecular interaction between the ligand and single receptor population. 4 Structure-activity relationships of selected prostanoids elucidated certain functional requirements for activation of adenylate cyclase.