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      Effects of Cl Substitution on Electrophysiological Properties, Ca 2+ Influx and Prolactin Secretion of Rat Lactotropes in vitro

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          In this study, we compared the effects of different chloride (Cl<sup>–</sup>) substitutes – methane sulfonate (CH<sub>3</sub>SO<sup>–</sup><sub>3</sub>), bromide (Br<sup>–</sup>), nitrate (NO<sup>–</sup><sub>3</sub>), thiocyanate (SCN<sup>–</sup>) and perchlorate (ClO<sup>–</sup><sub>4</sub>) – on the secretory activity and calcium current activation of rat lactotropes in primary culture. We observed that CH<sub>3</sub>SO<sup>–</sup><sub>3</sub> decreased basal prolactin (PRL) secretion. Br<sup>–</sup> had no effect, whereas the more lyotropic anions, such as NO<sup>–</sup><sub>3</sub>, SCN<sup>–</sup> and ClO<sup>–</sup><sub>4</sub>, increased basal PRL secretion. The latter three substitutes induced a significant shift in the voltage dependence of T-type calcium channel activation towards hyperpolarized values. However, this shift alone cannot explain the increase in secretion. Anion permeability studies also demonstrated that the organic anion CH<sub>3</sub>SO<sup>–</sup><sub>3</sub> was less permeant than Cl<sup>–</sup>, whereas monovalent inorganic anions were more permeant, with the following anion permeability sequence: SCN<sup>–</sup> > ClO<sup>–</sup><sub>4</sub> > NO<sup>–</sup><sub>3</sub> > Br<sup>–</sup>. In conclusion, deprivation of Cl<sup>–</sup> ions has converse consequences on basal and induced secretion; permeating anions result in a transient increase in intracellular Ca<sup>2+</sup> ions. This process involves voltage-dependent Ca<sup>2+</sup> channels. We propose that an alteration in intracellular anion concentrations may influence the activation of internal effectors such as G proteins or channel proteins and, therefore, interfere with exocytosis. These effects are correlated with an external action of lyotropic anions, particularly NO<sup>–</sup><sub>3</sub>, ClO<sup>–</sup><sub>4</sub> and SCN<sup>–</sup>, on the gating properties of T-type calcium channels, probably through changes in cell surface charges. The results demonstrate the modulatory effect of anions on the secretory activity of rat lactotropes and underline the specific role played by chloride in stimulus-secretion coupling.

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          Author and article information

          S. Karger AG
          November 1999
          17 November 1999
          : 70
          : 5
          : 332-342
          aDepartamento de Ciencias Fisiologicas, Facultad de Salud, Universidad del Valle, Cali, Colombia; bCNRS UMR 5543, Université Victor-Segalen Bordeaux-2, Bordeaux, France
          54494 Neuroendocrinology 1999;70:332–342
          © 1999 S. Karger AG, Basel

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          Page count
          Figures: 5, Tables: 2, References: 30, Pages: 11
          Pituitary Transduction


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