Small conductance Ca²⁺-activated K⁺ channels (SK channels) are heteromeric complexes of pore-forming α subunits and constitutively bound calmodulin (CaM). The binding of CaM is mediated in part by the electrostatic interaction between residues Arg-464 and Lys-467 of SK2 and Glu-84 and Glu-87 of CaM. Heterologous expression of the double charge reversal in SK2, SK2 R464E/K467E (SK2:64/67), did not yield detectable surface expression or channel activity in whole cell or inside-out patch recordings. Coexpression of SK2:64/67 with wild type CaM or CaM1,2,3,4, a mutant lacking the ability to bind Ca²⁺, rescued surface expression. In patches from cells coexpressing SK2:64/67 and wild type CaM, currents were recorded immediately following excision into Ca²⁺-containing solution but disappeared within minutes after excision or immediately upon exposure to Ca²⁺-free solution and were not reactivated upon reapplication of Ca²⁺-containing solution. Channel activity was restored by application of purified recombinant Ca²⁺-CaM or exposure to Ca²⁺-free CaM followed by application of Ca²⁺-containing solution. Coexpression of the double charge reversal E84R/E87K in CaM (CaM:84/87) with SK2:64/67 reconstituted stable Ca²⁺-dependent channel activity that was not lost with exposure to Ca²⁺-free solution. Therefore, Ca²⁺-independent interactions with CaM are required for surface expression of SK channels, whereas the constitutive association between the two channel subunits is not an essential requirement for gating.

Opioids are widely used as the pain reliever and also notorious for being addictive drugs. Sex differences in the opioid analgesia and addiction have been reported and investigated in human subjects and animal models. Yet, the molecular mechanism underlying the differences between males and females is still unclear. Here, we reviewed the literature describing the sex differences in analgesic responses and addiction liabilities to clinically relevant opioids. The reported interactions among opioids, estrogens, opioid receptors, and estrogen receptors are also evaluated. We postulate that the sex differences partly originated from the crosstalk among the estrogen and opioid receptors when stimulated by the exogenous opioids, possibly through common secondary messengers and the downstream gene transcriptional regulators.

We investigated the relationship between antidepressant use and the risk of subsequent dementia development. A population-based retrospective case-control analysis was conducted using the Taiwan National Health Insurance Research Database. From patients enrolled in the National Health Insurance program between 2005 and 2011, we identified 2 subsets: 5,394 cases, who had major depression in 1997-2004 and subsequently were diagnosed with dementia (ICD-9-CM code 290) in 2005-2011, and 5,232 controls, who had major depression in 2005-2011 but no dementia history. The proportional distributions of antidepressant use and comorbidities in the dementia case and nondementia control groups were compared. Univariable and multivariable logistic regression analyses were used to estimate the odds ratios (ORs) and 95% CIs for the association between dementia and antidepressant use. The dementia patients were more likely to have diabetes, hypertension, stroke, and head injury. The adjusted OR for dementia was 0.24 (95% CI, 0.22-0.27) in patients using tricyclics . By contrast, the use of selective serotonin reuptake inhibitors (SSRIs) (OR = 2.48; 95% CI, 2.27-2.71), monoamine oxidase inhibitors (MAOIs) (OR = 1.86; 95% CI, 1.47-2.36), heterocyclic antidepressants (OR = 1.44; 95% CI, 1.32-1.57), and other antidepressants (OR = 2.05; 95% CI, 1.85-2.27) was associated with an increased risk of dementia. Furthermore, as the cumulative dose was increased, tricyclic antidepressants reduced the risk of dementia, whereas SSRIs, MAOIs, heterocyclic antidepressants, and other antidepressants increased the risk of dementia. The incidence of dementia in patients is associated with antidepressant medication use. Treatment with tricyclic antidepressants was associated with a reduced risk of dementia, whereas treatment with SSRIs, MAOIs, heterocyclic antidepressants, and other antidepressants was associated with an increased risk of dementia.

Small conductance calcium-gated potassium (SK) channels share an overall topology with voltage-gated potassium (Kv) channels, but are distinct in that they are gated solely by calcium (Ca2+), not voltage. For Kv channels there is strong evidence for an activation gate at the intracellular end of the pore, which was not revealed by substituted cysteine accessibility of the homologous region in SK2 channels. In this study, the divalent ions cadmium (Cd2+) and barium (Ba2+), and 2-aminoethyl methanethiosulfonate (MTSEA) were used to probe three sites in the SK2 channel pore, each intracellular to (on the selectivity filter side of) the region that forms the intracellular activation gate of voltage-gated ion channels. We report that Cd2+ applied to the intracellular side of the membrane can modify a cysteine introduced to a site (V391C) just intracellular to the putative activation gate whether channels are open or closed. Similarly, MTSEA applied to the intracellular side of the membrane can access a cysteine residue (A384C) that, based on homology to potassium (K) channel crystal structures (i.e., the KcsA/MthK model), resides one amino acid intracellular to the glycine gating hinge. Cd2+ and MTSEA modify with similar rates whether the channels are open or closed. In contrast, Ba2+ applied to the intracellular side of the membrane, which is believed to block at the intracellular end of the selectivity filter, blocks open but not closed channels when applied to the cytoplasmic face of rSK2 channels. Moreover, Ba2+ is trapped in SK2 channels when applied to open channels that are subsequently closed. Ba2+ pre-block slows MTSEA modification of A384C in open but not in closed (Ba2+-trapped) channels. The findings suggest that the SK channel activation gate resides deep in the vestibule of the channel, perhaps in the selectivity filter itself.

Background: Abuse of addictive substances is a serious problem that has a significant impact on areas such as health, the economy, and public safety. Heroin use among young women of reproductive age has drawn much attention around the world. However, there is a lack of information on effects of prenatal exposure to opioids on their offspring. In this study, an animal model was established to study effects of prenatal exposure to opioids on offspring.Methods: Female pregnant Sprague-Dawley rats were sub-grouped to receive (1) vehicle, (2) 2-4 mg/kg morphine (1 mg/kg increment per week), (3) 7 mg/kg methadone, and (4) 3 mg/kg buprenorphine, subcutaneously, once or twice a day from E3 to E20. The experiments were conducted on animals 8-12 weeks old and with body weight between 250 and 350 g.Results: Results showed that prenatal exposure to buprenorphine caused higher mortality than other tested substance groups. Although we observed a significantly lower increase in body weight in all of the opioid-administered dams, the birth weight of the offspring was not altered in all treated groups. Moreover, no obvious behavioral abnormality or body-weight difference was noted during the growing period (8-12 weeks) in all offspring. When the male offspring received morphine injection twice a day for 4 days, the prenatally opioid-exposed rats more quickly developed a tolerance to morphine (as shown by the tail-flick tests), most notably the prenatally buprenorphine-exposed offspring. However, the tolerance development to methadone or buprenorphine was not different in offspring exposed prenatally to methadone or buprenorphine, respectively, when compared with that of the vehicle controlled group. Similar results were also obtained in the female animals.Conclusions: Animals prenatally exposed to morphine, methadone, or buprenorphine developed tolerance to morphine faster than their controlled mates. In our animal model, prenatal exposure to buprenorphine also resulted in higher mortality and much less sensitivity to morphine-induced antinociception than prenatal exposure to morphine or methadone. This indicates that buprenorphine in higher doses may not be an ideal maintenance drug for treating pregnant women. This study provides a reference in selecting doses for clinical usage in treating pregnant heroin addicts.