This review aims to clarify the relation between the ratio of omega-6 to omega-3 fatty acids and the development of depression. It is explained how these fatty acids are involved in the production of eicosanoids and how these fatty acids can affect the membrane fluidity, by their incorporation into membrane phospholipids. In addition, it is described how omega-3 derivatives are shown to regulate gene transcription. In view of the pathophysiology of depression, the mechanisms of how an altered ratio of omega-6 to omega-3 could be involved in depression are discussed. Possible mechanisms could include an increased production of pro-inflammatory cytokines, which can activate the HPA axis and a changed membrane fluidity, which potentially affects membrane bound enzymes, ion channels, receptor activity and neurotransmitter binding. In view of clinical trials, it is also discussed whether omega-3 supplementation could have a beneficial effect in the treatment of depressive patient. There are strong indications that an increased ratio of membrane omega-6 to omega-3 is involved in the pathogenesis of depression and so far, omega-3 supplementation has shown positive effects in clinical trials.

Several studies suggest the involvement of Na⁺ and HCO₃⁻ transport in the formation of cerebrospinal fluid. Two Na⁺-dependent HCO₃⁻ transporters were recently localized to the epithelial cells of the rat choroid plexus (NBCn1 and NCBE), and the mRNA for a third protein was also detected (NBCe2) (Praetorius J, Nejsum LN, and Nielsen S. Am J Physiol Cell Physiol 286: C601–C610, 2004). Our goal was to immunolocalize the NBCe2 to the choroid plexus by immunohistochemistry and immunogold electronmicroscopy and to functionally characterize the bicarbonate transport in the isolated rat choroid plexus by measurements of intracellular pH (pH_i) using a dual-excitation wavelength pH-sensitive dye (BCECF). Both antisera derived from COOH-terminal and NH₂-terminal NBCe2 peptides localized NBCe2 to the brush-border membrane domain of choroid plexus epithelial cells. Steady-state pH_i in choroidal cells increased from 7.03 ± 0.02 to 7.38 ± 0.02 ( n = 41) after addition of CO₂/HCO₃⁻ into the bath solution. This increase was Na⁺ dependent and inhibited by the Cl⁻ and HCO₃⁻ transport inhibitor DIDS (200 μM). This suggests the presence of Na⁺-dependent, partially DIDS-sensitive HCO₃⁻ uptake. The pH_i recovery after acid loading revealed an initial Na⁺ and HCO₃⁻-dependent net base flux of 0.828 ± 0.116 mM/s ( n = 8). The initial flux in the presence of CO₂/HCO₃⁻ was unaffected by DIDS. Our data support the existence of both DIDS-sensitive and -insensitive Na⁺- and HCO₃⁻-dependent base loader uptake into the rat choroid plexus epithelial cells. This is consistent with the localization of the three base transporters NBCn1, Na⁺-driven Cl⁻ bicarbonate exchanger, and NBCe2 in this tissue.

Although the biophysical fingerprints (ion selectivity, voltage-dependence, kinetics, etc) of Ca ²⁺ -activated Cl ⁻ currents are well established, their molecular identity is still controversial. Several molecular candidates have been suggested; however, none of them has been fully accepted. We have recently characterized a cGMP-dependent Ca ²⁺ -activated Cl ⁻ current with unique characteristics in smooth muscle cells. This novel current has been shown to coexist with a “classic” (cGMP-independent) Ca ²⁺ -activated Cl ⁻ current and to have characteristics distinct from those previously known for Ca ²⁺ -activated Cl ⁻ currents. Here, we suggest that a bestrophin, a product of the Best gene family, is responsible for the cGMP-dependent Ca ²⁺ -activated Cl ⁻ current based on similarities between the membrane currents produced by heterologous expressions of bestrophins and the cGMP-dependent Ca ²⁺ -activated Cl ⁻ current. This is supported by similarities in the distribution pattern of the cGMP-dependent Ca ²⁺ -activated Cl ⁻ current and bestrophin-3 (the product of Best-3 gene) expression in different smooth muscle. Furthermore, downregulation of Best-3 gene expression with small interfering RNA both in cultured cells and in vascular smooth muscle cells in vivo was associated with a significant reduction of the cGMP-dependent Ca ²⁺ -activated Cl ⁻ current, whereas the magnitude of the classic Ca ²⁺ -activated Cl ⁻ current was not affected. The majority of previous suggestions that bestrophins are a new Cl ⁻ channel family were based on heterologous expression in cell culture studies. Our present results demonstrate that at least 1 family member, bestrophin-3, is essential for a well-defined endogenous Ca ²⁺ -activated Cl ⁻ current in smooth muscles in the intact vascular wall.

The altered activity of the hypothalamic–pituitary–adrenal (HPA) axis is often observed in stress-related disorders. According to the literature, about 60% of patients with major depressive disorder elicit high levels of cortisol. It is still unclear why high cortisol levels are not observed in all patients. In this study, we used the chronic mild stress (CMS) rat model of depression, which is based on continuous exposure to unpredictable stressors, to track longitudinal changes in HPA function using fecal corticosterone metabolites (FCM) as a read out. The dexamethasone suppression test was used to assess negative feedback inhibition of the HPA axis. Our results show (1) a disturbance in diurnal corticosterone rhythm measured as fluctuations of the diurnal FCM peak, (2) differences in corticosterone levels between stress-susceptible and stress-resilient animals, (3) recovery of diurnal corticosterone rhythm after 8 weeks of CMS, and (4) alterations in sensitivity to dexamethasone in negative feedback regulation of corticosterone secretion during the time course of CMS. Thus, a disruption of HPA axis circadian rhythmicity coincides with the initial state in the development of depression-like behavior. This chronobiological abnormality, as well as the hypersecretion of corticosterone, is state, rather than trait, dependent.

Primary cultures of rat inner medullary collecting duct (IMCD) cells Na⁺dependently import [ ] across the basolateral membrane through an undefined transport protein. We used RT-PCR, immunoblotting, and immunohistochemistry to identify candidate proteins for this basolateral [ ] cotransport. The mRNA encoding the electroneutral [ ] cotransporter NBCn1 was detected as the only [ ] cotransporter in the rat inner medulla (IM) among the five characterized Na⁺-dependent [ ] transporters. The mRNA of a yet uncharacterized transporter-like protein, BTR1, was also present in the IM, but its expression in microdissected tubules seemed restricted to the thin limbs of Henle's loop. Immunoblotting confirmed the presence of NBCn1 as an ∼180-kDa protein of the rat IM. Anti-NBCn1 immunolabeling was confined to the basolateral plasma membrane domain of IMCD cells in the papillary two-thirds of the IM. Consistent with the presence of NBCn1, IMCD cells possessed stilbene-insensitive, Na⁺- and [ ]-dependent pH recovery after acidification, as assessed by fluorescence microscopy using a pH-sensitive intracellular dye. In furosemide-induced alkalotic rats, NBCn1 protein abundance was decreased in both the IM and inner stripe of outer medulla (ISOM) as determined by immunoblotting and immunohistochemistry. In contrast, NBCn1 abundance in the IM and ISOM was unchanged in NaHCO₃-loaded animals, and the NBCn1 abundance increased only in the ISOM after NH₄Cl loading. In conclusion, NBCn1 is a basolateral [ ] cotransporter of IMCD cells and is differentially regulated in IMCD and medullary thick ascending limb.