In this study, we compared the effects of different chloride (Cl^–) substitutes – methane sulfonate (CH₃SO^–₃), bromide (Br^–), nitrate (NO^–₃), thiocyanate (SCN^–) and perchlorate (ClO^–₄) – on the secretory activity and calcium current activation of rat lactotropes in primary culture. We observed that CH₃SO^–₃ decreased basal prolactin (PRL) secretion. Br^– had no effect, whereas the more lyotropic anions, such as NO^–₃, SCN^– and ClO^–₄, 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 CH₃SO^–₃ was less permeant than Cl^–, whereas monovalent inorganic anions were more permeant, with the following anion permeability sequence: SCN^– > ClO^–₄ > NO^–₃ > Br^–. In conclusion, deprivation of Cl^– ions has converse consequences on basal and induced secretion; permeating anions result in a transient increase in intracellular Ca²⁺ ions. This process involves voltage-dependent Ca²⁺ 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^–₃, ClO^–₄ and SCN^–, 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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Human decidual cells synthesize and release decidual PRL (dPRL) immunologically and biochemically identical to human pituitary PRL. However, stimulators and inhibitors of PRL secretion such as TRH, bromocriptine or dopamine have no effect on dPRL release. The evidence for the involvement of Ca2+ in dPRL release is based on contradictory or unclear data. Since little is known about Ca2+ movement in human decidual cells we studied the membrane Ca2+ conductance of cultured decidual cells using the patch-clamp technique in the whole-cell configuration. We report the existence of Ca(2+)-dependent action potentials triggered by hyperpolarizing or depolarizing pulses and blocked by cobalt (Co2+; 5 mM). Spontaneous action potentials were observed in the cell-attached mode and found also to be Co(2+)-sensitive. A tetrodotoxin-insensitive and Ca(2+)-dependent rapidly inactivating inward current was investigated in voltage clamp. Its activation threshold was between -60 and -45 mV. Indo-1 measurements of free intracellular Ca2+ concentrations ([Ca2+]i, 169 +/- 14 nM and 141 +/- 8 nM in short-term culture vs. 149 +/- 5 nM in cells cultured for 3-6 days) showed that decidual cells have spontaneous transient fluctuations of [Ca2+]i and that [Ca2+]i was decreased by Ca2+ channel blockers. The existence of Ca2+ movements in decidual cells in culture is thus demonstrated. The occurrence of action potentials in decidual cells derived from fibroblasts, reputed to be inexitable cells, is an interesting biological observation. However, Ca2+ is not involved in the short-term release of PRL by decidual cells, and its effects on long-term secretion still requires further investigation.

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