Determination of transmitter function by neuronal activity

The role of neuronal activity in the determination of transmitter function was studied in cultures of dissociated sympathetic neurons from newborn rat superior cervical ganglia. Cholinergic and adrenergic differentiation were assayed by incubating the cultures with radioactive choline and tyrosine and determining the rate of synthesis and accumulation of labelled acetylcholine and catecholamines. As in previous studies, pure neuronal cultures grown in control medium displayed much lower ratios of acetylcholine synthesis to catecholamine synthesis than did sister cultures grown in medium previously conditioned by incubation on appropriate nonneuronal cells (conditioned medium). However, here we report that neurons treated with the depolarizing agents elevated K(+) or veratridine, or stimulated directly with electrical current, either before or during application of conditioned medium, displayed up to 300-fold lower acetylcholine/catecholamine ratios than they would have without depolarization, and thus remained primarily adrenergic. Elevated K(+) and veratridine produced this effect on cholinergic differentiation without significantly altering neuronal survival. Because depolarization causes Ca(2+) entry in a number of cell types, the effects of several Ca(2+) agonists and antagonists were investigated. In the presence of the Ca(2+) antagonists D600 or Mg(2+), K(+) did not prevent the induction of cholinergic properties by conditioned medium. Thus depolarization, either steady or accompanying activity, is one of the factors determining whether cultured sympathetic neurons become adrenergic or cholinergic, and this effect may be mediated by Ca(2+).

Effects of colchicine on cyclic AMP levels in human leukocytes

The increase in human leukocyte adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels seen in response to various substances was markedly potentiated by colchicine and other agents that affect microtubule assembly. Addition of dl-isoproterenol (2 muM) or prostaglandin E(1) (10 muM), together with the phosphodiesterase inhibitor isobutylmethylxanthine (1 mM), caused a much greater increase in cyclic AMP in colchicine-pretreated cells than in control cells. With isoproterenol (2 muM) plus isobutylmethylaxanthine (1 mM), cyclic AMP levels rose about 3-fold but, in combination with colchicine, these drugs caused a more than 15-fold increase in cyclic AMP. The effects of colchicine were both time- and dose-dependent; they could be seen within 1 min after addition of colchicine or at concentrations as low as 10 nM. In addition to its potentiation of hormonally induced increases in cyclic AMP levels, colchicine also potentiated the effect of isobutylmethylxanthine alone on leukocyte cyclic AMP levels. Vinblastine, vincristine, podophyllotoxin, and oncodazole all had effects similar to those of colchicine but lumicolchicine did not. The data suggest that cytoplasmic microtubules interact with the leukocyte plasma membrane to impose constraints on the expression of hormone-sensitive adenylate cyclase; the therapeutic effects of colchicine may depend in part upon the relaxation of such constraints. Moreover, the synergism described here between colchicine-like agents and hormones is of potential therapeutic importance in clinical conditions in which either alkaloid or hormone has been useful separately.

Selection for neuroblastoma cells that synthesize certain transmitters

A selection procedure was devised for neurons and related cells that depends upon the ability of the cells to synthesize certain amine neurotransmitters. The rationale for selection is that tyrosine is an essential amino acid for most mammalian cells and that three enzymes from mammalian sources can catalyze the synthesis of tyrosine: phenylalanine hydroxylase (EC 1.14.16.1), tyrosine hydroxylase (EC 1.14.16.2), and tryptophan hydroxylase (EC 1.14.16.4). Tyrosine hydroxylase is found predominantly in adrenergic neurons and related cells that synthesize dopamine, norepinephrine, and epinephrine, and tryptophan hydroxylase in cells synthesizing serotonin or melatonin. Only 1 out of 70,000 uncloned mouse neuroblastoma cells grew well in the absence of tyrosine. Approximately 50% of the cell lines obtained by selection had tyrosine hydroxylase activity. This selection procedure thus provides a simple means of obtaining cell lines of neural origin on the basis of their ability to synthesize putative transmitters.

The effects of insulin, glucose and catecholamines on some blood minerals in sheep

Intravenous injection of insulin, 0.5 i.u./kg, was followed by a decrease in plasma magnesium. It is earlier known that insulin sometimes lowers the blood magnesium level, and the mechanism behind this effect is said to be an increased tissue uptake of magnesium. Glucose infusion did not change plasma magnesium, whereas norepinephrine and epinephrine caused a slight reduction. Insulin at the dose of 1 i.u./kg reduced plasma calcium in intact sheep. In thyroidectomized sheep the same dose caused a rise in plasma calcium. It is suggested that insulin caused hypercalcaemia in the thyroidectomized sheep by increasing the rate of bone resorption, and that the decrease in plasma calcium observed in the intact sheep was due to release of calcitonin to such an extent that the bone resorbing effect of insulin was blocked. Insulin also lowered plasma inorganic phosphorus in the thyroidectomized sheep.

Identification of the cardiac beta-adrenergic receptor protein: solubilization and purification by affinity chromatography

A protein that binds catecholamines with a specificity parallel to that of their in vivo effects on cardiac contractility (isoproterenol > epinephrine or norepinephrine > dopamine > dihydroxyphenylalanine) was solubilized from a microsomal fraction of canine ventricular myocardium. The binding protein was purified 500 to 800-fold by solubilization and subsequent affinity chromatography with conjugates of norepinephrine linked to agarose beads. Purified beta-adrenergic binding protein exists in two forms, corresponding to molecular weights of 40,000 and 160,000. The purified material has a single association constant, 2.3 x 10(5) liters/mol (as compared to two association constants, 10(7) and 10(6) liters/mol, for the binding protein in particulate form) but retains the identical binding specificity for beta-adrenergic drugs and antagonists.

Dopamine- -hydroxylase activity in mouse neuroblastoma tumors and in cell cultures

Dopamine-beta-hydroxylase activity is present in mouse neuroblastoma C-1300 tumors. The activity is proportional to the weight of the tumor. Serum activity is markedly increased in mice that bear the tumors. Treatment of mice with 5-bromodeoxyuridine causes marked inhibition of tumor growth and decrease of dopamine-beta-hydroxylase activity in the serum. The histochemical studies reveal that 1-5% of the cells in mouse C-1300 neuroblastoma tumors contain catecholamines and that catecholamine-containing processes terminate mainly around blood vessels of the tumor. Dopamine-beta-hydroxylase is present in clonal neuroblastoma cell lines. The cell line with the greater tendency to form axon-like processes has a higher activity of this enzyme.

Accumulation of adenosine 3':5'-cyclic monophosphate in clonal glial cells: labeling of intracellular adenine nucleotides with radioactive adenine

The accumulation of endogenous adenosine 3':5'-cyclic phosphate (cAMP) and of [(14)C]cAMP, derived from nucleotides labeled by prior incubation of cells with [(14)C]adenine, has been investigated in four glial cell lines from rats. The following results are similar to data reported for brain slices: (i) rat glial cells contain a system that readily incorporates [(14)C]adenine into nucleotides that serve as precursors for cAMP. (ii) norepinephrine stimulates accumulation of both [(14)C]cAMP and endogenous cAMP, and (iii) the phosphodiesterase inhibitors, papaverine and isobutylmethylxanthine, are effective in enhancing the stimulatory effect of norepinephrine. In contrast to results reported for brain slices, histamine, veratridine, and adenosine, the purine either alone or with a biogenic amine, do not cause an enhanced accumulation of cAMP in rat glial cells, and repetitive accumulations of cAMP can be elicited during a series of restimulations of the cells with norepinephrine. The magnitude of the accumulation of cAMP elicited by the catecholamine decreases markedly by the fifth restimulation in the absence of, but only slightly in the presence of, papaverine. In glial cells, a large portion of the [(14)C]adenine is incorporated into intracellular compounds that do not serve as precursors of [(14)C]cAMP.

Decrease of the 3,4-dihydroxyphenylalanine (DOPA) decarboxylase activities in human erythrocytes and mouse tissues after administration of DOPA

Human erythrocytes have been found to contain appreciable amounts of DOPA decarboxylase (EC 4.1.1.26) activity. The enzyme activity in erythrocytes from patients with Parkinson's disease who were treated with DOPA was significantly lower than that of untreated patients and of normal individuals. Administration of the drug to mice led to a marked decrease of DOPA decarboxylase in liver and kidney, but not of the brain enzyme. The findings thus indicate that administration of DOPA leads to a decrease in peripheral DOPA decarboxylase, an effect that is expected to be of benefit in DOPA therapy of patients with Parkinson's disease. Peripheral DOPA decarboxylase concentration also decreases in mice after short periods of fasting; the findings suggest that the peripheral enzyme activities may be affected by various nutritional and perhaps hormonal influences, which may be partially responsible for the observed fluctuations in the motor abilities of Parkinsonian patients receiving constant doses of the drug. Study of DOPA decarboxylase activity in erythrocytes may be useful in following changes in patients receiving DOPA therapy and may also be of general interest and value in investigations of catecholamine metabolism in man.