U-Shape Suppressive Effect of Phenol Red on the Epileptiform Burst Activity via Activation of Estrogen Receptors in Primary Hippocampal Culture

Phenol red is widely used in cell culture as a pH indicator. Recently, it also has been reported to have estrogen-like bioactivity and be capable of promoting cell proliferation in different cell lines. However, the effect of phenol red on primary neuronal culture has never been investigated. By using patch clamp technique, we demonstrated that hippocampal pyramidal neurons cultured in neurobasal medium containing no phenol red had large depolarization-associated epileptiform bursting activities, which were rarely seen in neurons cultured in phenol red-containing medium. Further experiment data indicate that the suppressive effect of the phenol red on the abnormal epileptiform burst neuronal activities was U-shape dose related, with the most effective concentration at 28 µM. In addition, this concentration related inhibitory effect of phenol red on the epileptiform neuronal discharges was mimicked by 17-β-estradiol, an estrogen receptor agonist, and inhibited by ICI-182,780, an estrogen receptor antagonist. Our results suggest that estrogen receptor activation by phenol red in the culture medium prevents formation of abnormal, epileptiform burst activity. These studies highlight the importance of phenol red as estrogen receptor stimulator and cautions of careful use of phenol red in cell culture media.     

Heterogeneity of the Glyoxylate-Condensing Enzymes.

Wegener, Warner S. (Albert Einstein Medical Center, Philadelphia, Pa.), Henry C. Reeves, and Samuel J. Ajl. Heterogeneity of the glyoxylate-condensing enzymes. J. Bacteriol. 90:594-598. 1965.-Evidence is presented that the enzymatic condensations of glyoxylate with acetyl-CoA (malate synthase), propionyl-CoA (alpha-hydroxyglutarate synthase), butyryl-CoA (beta-ethylmalate synthase), and valeryl-CoA (beta-n-propylmalate synthase) are catalyzed by different enzymes. The possibility that these activities resulted from a single enzyme possessing a broad fatty acid acyl-CoA substrate specificity was ruled out. The latter was suggested by the fact that cells grown on a number of short-chain fatty acids exhibited all the above activities. The conclusion that these reactions are catalyzed by different enzymes is based on the following considerations: (i) the enzymes can be differentially inactivated by heat; (ii) under various growth conditions, where all the condensing enzymes are present, their respective activities do not show a constant ratio, as would be expected if they were catalyzed by a single enzyme; and (iii) under appropriate growth conditions, one or more of these enzymes has been shown to be present to the exclusion of others.