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Voltage-gated K+ channels play an essential role in the production of action potential activity by excitable cells. Recent studies have suggested that expression of K+ channel genes may be regulated by stimuli that affect electrical activity. Elevating the concentration of extracellular KCl causes membrane depolarization and, thus, is widely used for studying electrical activity-dependent changes in neurons, muscle, and endocrine cells. Here we show that elevated KCl decreases Kv1.5 K+ channel mRNA expression in clonal pituitary cells without affecting Kv1.4 and Kv2.1 mRNA levels. K+ channel blockers, which cause depolarization, also produce down-regulation of Kv1.5 mRNA, while NaCl addition had no effect. Thus, the effect of KCl is mediated by K(+)-induced membrane depolarization. Unlike many known effects of K+, down-regulation of Kv1.5 mRNA does not require Ca2+ or Na+ influx, or Na(+)-H+ exchange. Furthermore, the decrease in Kv1.5 mRNA expression is due to inhibition of channel gene transcription and persists after inhibition of protein synthesis, excluding a role for induction of intermediary regulatory proteins. Finally, immunoblots with antibody specific for the Kv1.5 polypeptide show that depolarization for 8 h reduces the expression of Kv1.5 channel protein. The decrease in K+ channel protein expression caused by depolarization-induced Ca(2+)-independent inhibition of Kv1.5 gene transcription may produce a long-term enhancement of pituitary cell excitability and secretory activity.

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Allergic contact dermatitis (ACD) is a widespread concern in which sensitization occurs to low molecular weight chemicals. Currently, animal and human assays are used to identify chemicals with potential to cause ACD. MultiCASE, a computer based structure-activity relational system was employed to evaluate a data base of contact sensitizers and identify structural determinants (biophores) associated with sensitization. The data base was derived from reports of animal and human studies and consisted of 1034 chemicals of which 317 were classified as sensitizers (extreme, strong, moderate, or weak), 22 chemicals had marginal (questionable) activity, and 695 were inactive. MultiCASE identified 49 biophores with related expanded fragments which accounted for the activity of all active chemicals. The major biophores consisted of : 1) a nitrogen double-bonded to a carbon or a nitrogen; 2) substituted aromatic structures; 3) thiol and disulfide containing fragments; and 4) electrophilic moieties. Modulators of each biophore, which either augmented or decreased potency, included additional structural fragments, two dimensional distance descriptors, as well as physico-chemical characteristics. Internal evaluation of the data base indicated the sensitivity was 99.6%, and the specificity of the data set was 99.4%. Prediction of the activity of chemicals not in the learning set gave a concordance of 90.2% with experimental results. These findings demonstrate the ability of MultiCASE to identify contact sensitizers and suggest its ability to screen chemicals for their potential to produce ACD.Key words: Allergic contact dermatitis; SAWQSAR; MultiCASE; structural alerts ketones, metals, nitrogen-containing heterocycles, and oxygencontaining heterocycles, among others. Payne and Walsh [4] developed a list of structural alerts based on the requirement for protein reactivity that included: alkylating, acylating, and arylating agents; Michael addition electrophiles; thiol exchange compounds; and free radical generators; among others. Many of the existing SAR systems have incorporated physico-chemical considerations [5, 61. The mathematical model described by Roberts and Basketter [6] for alkyl transfer agents has incorporated both a rate constant for reaction of a chemical with a nucleophile, and a lipophilicity factor (log P).The Multiple Computer Automated Structure Evaluation (Multi-CASE) system [9] differs from other published SAR systems in that it assumes no mechanism of toxicity. Rather, it automatically generates and identifies fragments which are statistically associated with activity (biophores). In the context of toxicological processes, biophores represent structural alerts [9]. MultiCASE will group compounds containing biophores, thereby suggesting a similarity in their mechanism of activity. The system also differs from other SAR models by identifying activating and deactivating fragments. Physicochemical factors are also considered when attributing the degree of activity.MultiCASE has been used to identify s...