Glucocorticoid block of protein kinase C signalling in mouse pituitary corticotroph AtT20 D16:16 cells

Potential benefits of Yoga in pregnancy-related complications during the COVID-19 pandemic and implications for working women

BACKGROUND

Pregnancy is a vulnerable period of growth and enrichment along with many physiological and psychological challenges. These changes can lead to complications if compounded by external stress and anxiety. COVID-19 has emerged as a chief stressor among the general population and is a serious threat among vulnerable populations. Therefore, there is a need for stress management tools, such as Yoga and physical exercises, both at home and at work. These can be adopted during the pandemic with proper maintenance of social distancing.

OBJECTIVE

To evaluate and compile literature that has reported the health outcomes of Yoga intervention on pregnancy at the workplace and analyzes both the restrictions as well as advantages of its beneficial effects in comparison to physical exercises.

METHODOLOGY

A comprehensive literature review was conducted utilizing PubMed and Google Scholar. The keywords used for the search include "Yoga", "work", "complications", "physical exercise", "drugs" and "COVID" indifferent permutations and combinations with "pregnancy". We compiled the literature with respect to pregnancy complications and the effects of drugs, physical activity and Yoga for preventing these complications.

RESULTS

We noted that pregnancy-related complications are becoming more prevalent because of a sedentary lifestyle, restricted physical activity and growing stress. In such situations, a home or workplace Yoga protocol can combine both exercise and mindfulness-based alleviation of anxiety for both working and non-working women.

CONCLUSION

Yoga can be effective for combating stress and anxiety besides boosting immunity in pregnant working women confronted with the COVID-19 pandemic.

Impairment of neurovascular coupling in Type 1 Diabetes Mellitus in rats is prevented by pancreatic islet transplantation and reversed by a semi-selective PKC inhibitor

Streptozotocin (STZ)-induced chronic hyperglycemia has a detrimental effect on neurovascular coupling, linked to increased PKC-mediated phosphorylation and PKC isoform expression changes. Here, we sought to determine whether: 1) selective PKC-α/β/γ inhibitor, GF109203X, could reverse the effects of chronic hyperglycemia on cerebrovascular reactivity; 2) pancreatic islet transplantation could prevent the development of cerebrovascular impairment seen in a rat model of Type 1 Diabetes. We studied the effect of GF109203X in diabetic (DM), non-diabetic (ND), and transplanted (TR) Lewis rats during either sciatic nerve stimulation (SNS) or the topical applications of the large-conductance Ca²⁺-operated K⁺(BK_Ca) channel opener, NS1619, or the K⁺ inward rectifier (Kir) channel agonist, KCl. Pial arteriole diameter changes were monitored using a closed cranial window in vivo microscopy technique. The pial arteriole dilatory response associated with SNS was decreased by ~45%, when comparing DM vs either ND or TR rats. Also, pial arteriolar dilations to topical KCl and NS1619 were largely attenuated in DM rats, but not in ND or TR animals. These responses were completely restored by the acute application of GF109203X to the brain surface. The PKC inhibitor had no effect on vascular responses in normoglycemic and TR animals. In conclusion, DM-associated chronic impairment of neurovascular coupling may be readily reversed by a PKC-α/β/γ inhibitor or prevented via pancreatic islet transplantation. We believe that specific PCK isoforms (α/β/γ) are mechanistically linked to the neurovascular uncoupling seen with hyperglycemia.

Prenatal dexamethasone exposure in rats results in long-term epigenetic histone modifications and tumour necrosis factor-α production decrease

Glucocorticoid (GC) is often given when preterm delivery is expected. This treatment is successful in stimulating the development of the fetal lung. However, reports and related research regarding the prolonged effects of prenatal GC on the development of immunity are very limited. Some data, derived from infants whose mothers were given immunosuppressants during pregnancy for the treatment of autoimmune disorders, suggest that prenatal exposure to GC may have only a limited effect on the development of the immune system. What is unknown is whether the immune modulation effects of prenatal GC might appear at a later childhood stage and beyond. Here we evaluated the immune programming influenced by prenatal GC. Pregnant Sprague-Dawley rats received dexamethasone (DEX; 0.1 mg/kg/day) or saline at gestational days 14-20. Male offspring were killed at day 7 or day 120 after birth. Spleens were collected for immune study. Of the inflammation mediators, matrix metalloproteinase-9, tumour necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor mRNAs decreased in the prenatal DEX group at an early stage after birth. Upon concanavalin A stimulation, prenatal DEX treatment reduced TNF-α production, but not interferon-γ production, by splenocytes at day 120 after birth compared with the vehicle group. Decreased levels of active chromatin signs (acetylation of histone H3 lysines, H3K4me1/3, and H3K36me3) in TNF-α promoter were compatible with the expressions of TNF-α. Our results suggest that prenatal DEX has a profound and lasting impact on the developing immune system even to the adult stage. Epigenetic histone modifications regulate TNF-α expression following prenatal DEX in rats.

Complex modulation of the expression of PKC isoforms in the rat brain during chronic type 1 diabetes mellitus

We previously demonstrated that chronic hyperglycemia has a detrimental influence on neurovascular coupling in the brain-an effect linked to an alteration in the protein kinase C (PKC)-mediated phosphorylation pattern. Moreover, the activity of PKC was increased, in diabetic rat brain, in a tissue fraction composed primarily of the superficial glia limitans and pial vessels, but trended toward a decrease in cerebral cortical gray matter. However, that study did not examine the expression patterns of PKC isoforms in the rat brain. Thus, in a rat model of streptozotocin (STZ)-induced chronic type 1 diabetes mellitus (T1DM), and in non-diabetic (ND) controls, two hypotheses were addressed. First, chronic T1DM is accompanied by changes in the expression of PKC-α, βII, γ, δ, and ε Second, those changes differ when comparing cerebral cortex and glio-pial tissue. In addition, we analyzed the expression of a form of PKC-γ, phosphorylated on threonine 514 (pT514-PKC-γ), as well as the receptor for activated C kinase 1 (RACK1). The expression pattern of different PKC isoforms was altered in a complex and tissue-specific manner during chronic hyperglycemia. Notably, in the gray matter, PKC-α expression significantly decreased, while pT514-PKC-γ expression increased. However, PKC-βII, -γ, -δ, -ε, and RACK1 expressions did not change. Conversely, in glio-pial tissue, PKC-α and RACK1 were upregulated, whereas PKC-γ, pT514-PKC-γ, and PKC-ε were downregulated. PKC-βII, and PKC-δ, were unchanged. These findings suggest that the PKC activity increase previously seen in the glio-pial tissue of diabetic rats may be due to the selective upregulation of PKC-α, and ultimately lead to the impairment of neurovascular coupling.

Neuroendocrine control of maternal stress responses and fetal programming by stress in pregnancy

The major changes in highly dynamic neuroendocrine systems that are essential for establishing and maintaining pregnancy are outlined from studies on rodents. These changes optimise the internal environment to provide the life support system for the placenta, embryo and fetus. These include automatic prevention of further pregnancy, blood volume expansion, increased appetite and energy storage. The brain regulates these changes, in response to steroid (estrogens, progesterone) and peptide (lactogens, relaxin) hormone signals. Activation of inhibitory endogenous opioid mechanisms in the brain in late pregnancy restrains premature secretion of oxytocin, and attenuates hypothalamo-pituitary-adrenal (HPA) responses to stress. This opioid mechanism is activated by allopregnanolone, a neuroactive progesterone metabolite. The significance of reduced HPA axis responses in shifting maternal metabolic balance, and in protecting the fetuses from adverse programming of HPA axis stress responsiveness and anxious behaviour in later life is critically discussed. Experimental studies showing sex-dependent fetal programming by maternal stress or glucocorticoid exposure in late pregnancy are reviewed. The possibility of over-writing programming in offspring through neurosteroid administration is discussed. The impact of maternal stress on placental function is considered in the context of reconciling studies that show offspring programming by stress in very early or late pregnancy produce similar phenotypes in the offspring.

Ion channels and signaling in the pituitary gland

Endocrine pituitary cells are neuronlike; they express numerous voltage-gated sodium, calcium, potassium, and chloride channels and fire action potentials spontaneously, accompanied by a rise in intracellular calcium. In some cells, spontaneous electrical activity is sufficient to drive the intracellular calcium concentration above the threshold for stimulus-secretion and stimulus-transcription coupling. In others, the function of these action potentials is to maintain the cells in a responsive state with cytosolic calcium near, but below, the threshold level. Some pituitary cells also express gap junction channels, which could be used for intercellular Ca(2+) signaling in these cells. Endocrine cells also express extracellular ligand-gated ion channels, and their activation by hypothalamic and intrapituitary hormones leads to amplification of the pacemaking activity and facilitation of calcium influx and hormone release. These cells also express numerous G protein-coupled receptors, which can stimulate or silence electrical activity and action potential-dependent calcium influx and hormone release. Other members of this receptor family can activate calcium channels in the endoplasmic reticulum, leading to a cell type-specific modulation of electrical activity. This review summarizes recent findings in this field and our current understanding of the complex relationship between voltage-gated ion channels, ligand-gated ion channels, gap junction channels, and G protein-coupled receptors in pituitary cells.

Hypothalamic-pituitary-adrenal axis hyporesponsiveness to restraint stress in mice deficient for large-conductance calcium- and voltage-activated potassium (BK) channels

Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, releasing ACTH from the anterior pituitary gland and glucocorticoids from the adrenal cortex. Stress also activates the sympathetic nervous system, evoking adrenaline release from the adrenal medulla. Large-conductance calcium- and voltage-activated potassium (BK) channels have been implicated in regulation of cellular excitability in these systems. Here, we examine the functional role of BK channels in HPA axis regulation in vivo using female mice genetically deficient (BK(-/-)) for the pore-forming subunits of BK channels. BK(-/-) phenotype in the HPA was confirmed by immunohistochemistry, Western blot analysis, and corticotrope patch-clamp recording. Restraint stress-induced plasma concentrations of ACTH and corticosterone were significantly blunted in BK(-/-) mice compared with wild type (WT) controls. This stress hyporesponsiveness was associated with reduced activation of hypothalamic paraventricular nucleus (PVN) neurons. Basal expression of CRH, but not arginine vasopressin mRNA in the PVN was significantly lower in BK(-/-) mice compared with WT controls. Total anterior pituitary ACTH peptide content, but not proopiomelanocortin mRNA expression or corticotrope number, was significantly reduced in BK(-/-) mice compared with WT. However, anterior pituitary corticotropes from BK(-/-) mice fully supported ACTH output, releasing a significantly greater proportion of stored ACTH in response to secretagogue in vitro compared with WT. These results support an important role for BK channels in both the neural circuitry and endocrine output of the HPA axis and indicate that the stress hyporesponsiveness in BK(-/-) mice primarily results from reduced activation of hypothalamic PVN neurosecretory neurons.

Large-conductance calcium-activated potassium channel activity is absent in human and mouse neutrophils and is not required for innate immunity

Large-conductance Ca(2+)-activated K(+) (BK) channels are reported to be essential for NADPH oxidase-dependent microbial killing and innate immunity in leukocytes. Using human peripheral blood and mouse bone marrow neutrophils, pharmacological targeting, and BK channel gene-deficient (BK(-/-)) mice, we stimulated NADPH oxidase activity with 12-O-tetradecanoylphorbol-13-acetate (PMA) and performed patch-clamp recordings on isolated neutrophils. Although PMA stimulated NADPH oxidase activity as assessed by O(2)(-) and H(2)O(2) production, our patch-clamp experiments failed to show PMA-activated BK channel currents in neutrophils. In our studies, PMA induced slowly activating currents, which were insensitive to the BK channel inhibitor iberiotoxin. Instead, the currents were blocked by Zn(2+), which indicates activation of proton channel currents. BK channels are gated by elevated intracellular Ca(2+) and membrane depolarization. We did not observe BK channel currents, even during extreme depolarization to +140 mV and after elevation of intracellular Ca(2+) by N-formyl-L-methionyl-L-leucyl-phenylalanine. As a control, we examined BK channel currents in cerebral and tibial artery smooth muscle cells, which showed characteristic BK channel current pharmacology. Iberiotoxin did not block killing of Staphylococcus aureus or Candida albicans. Moreover, we addressed the role of BK channels in a systemic S. aureus and Yersinia enterocolitica mouse infection model. After 3 and 5 days of infection, we found no differences in the number of bacteria in spleen and kidney between BK(-/-) and BK(+/+) mice. In conclusion, our experiments failed to identify functional BK channels in neutrophils. We therefore conclude that BK channels are not essential for innate immunity.

Calcium-activated potassium channel of the tobacco hornworm, Manduca sexta: molecular characterization and expression analysis

Large-conductance calcium- and voltage-gated potassium channels (BK or Slowpoke) serve as dynamic integrators linking electrical signaling and intracellular activity. These channels can mediate many different Ca2+-dependent physiological processes including the regulation of neuronal and neuroendocrine cell excitability and muscle contraction. To gain insights into the function of BK channels in vivo, we isolated a full-length cDNA encoding the alpha subunit of a Slowpoke channel from the tobacco hornworm, Manduca sexta (msslo). Amino acid sequence comparison of the deduced Manduca protein revealed at least 80% identity to the insect Slo channels. The five C-terminal alternative splice regions are conserved, but the cloned cDNA fragments contained some unique combinations of exons E, G and I. Our spatial profile revealed that transcript levels were highest in skeletal muscle when compared with the central nervous system (CNS) and visceral muscle. The temporal profile suggested that msslo expression is regulated developmentally in a tissue- and regional-specific pattern. The levels of msslo transcripts remain relatively constant throughout metamorphosis in the CNS, transiently decline in the heart and are barely detectable in the gut except in adults. A dramatic upregulation of msslo transcript levels occurs in thoracic but not abdominal dorsal longitudinal body wall muscles (DLM), suggesting that the msSlo current plays an important role in the excitation or contractile properties of the phasic flight muscle. Our developmental profile of msslo expression suggests that msSlo currents may contribute to the changes in neural circuits and muscle properties that produce stage-specific functions and behaviors.

Conditional protein phosphorylation regulates BK channel activity in rat cerebellar Purkinje neurons

Large conductance calcium- and voltage-activated potassium (BK) channels are widely expressed in the mammalian central nervous system. Although the activity of BK channels in endocrine and vascular cells is regulated by protein kinases and phosphatases associated with the channel complex, direct evidence for such modulation in neurons is largely lacking. Single-channel analysis from inside-out patches isolated from the soma of dissociated rat cerebellar Purkinje neurons demonstrated that the activity of BK channels is regulated by multiple endogenous protein kinases and protein phosphatases in the membrane patch. The majority of BK channels were non-inactivating and displayed a 'low' activity phenotype determined at +40 mV and 1 muM intracellular free calcium. These channels were activated by cAMP-dependent protein kinase (PKA) associated with the patch and the extent of PKA activation was limited by an opposing endogenous type 2A-like protein phosphatase (PP2A). Importantly, PKA activation was dependent upon the prior phosphorylation status of the BK channel complex dynamically controlled by protein kinase C (PKC) and protein phosphatase 1 (PP1). In contrast, Purkinje cells also displayed a low proportion of non-inactivating BK channels with a 'high' activity under the same recording conditions and these channels were inhibited by endogenous PKA. Our data suggest that: (1) multiple endogenous protein kinases and phosphatases functionally couple to the BK channel complex to allow conditional modulation of BK channel activity in neurons, and (2) native, phenotypically distinct, neuronal BK channels are differentially sensitive to PKA-dependent phosphorylation.

Dexamethasone induces rapid serine-phosphorylation and membrane translocation of annexin 1 in a human folliculostellate cell line via a novel nongenomic mechanism involving the glucocorticoid receptor, protein kinase C, phosphatidylinositol 3-kinase, and mitogen-activated protein kinase

Our recent studies on rat pituitary tissue suggest that the annexin 1 (ANXA1)-dependent inhibitory actions of glucocorticoids on ACTH secretion are effected via a paracrine mechanism that involves protein kinase C (PKC)-dependent translocation of a serine-phosphorylated species of ANXA1 (Ser-P-ANXA1) to the plasma membrane of the nonsecretory folliculostellate cells. In the present study, we have used a human folliculostellate cell line (PDFS) to explore the signaling mechanisms that cause the translocation of Ser-P-ANXA1 to the membrane together with Western blot analysis and flow cytometry to detect the phosphorylated protein. Exposure of PDFS cells to dexamethasone caused time-dependent increases in the expression of ANXA1 mRNA and protein, which were first detected within 2 h of steroid contact. This genomic response was preceded by the appearance within 30 min of substantially increased amounts of Ser-P-ANXA1 and by translocation of the phosphorylated protein to the cell surface. The prompt membrane translocation of Ser-P-ANXA1 provoked by dexamethasone was inhibited by the glucocorticoid receptor, antagonist, mifepristone, but not by actinomycin D or cycloheximide, which effectively inhibit mRNA and protein synthesis respectively in our preparation. It was also inhibited by a nonselective PKC inhibitor (PKC(9-31)), by a selective inhibitor of Ca(2+)-dependent PKCs (Go 6976) and by annexin 5 (which sequesters PKC in other systems). In addition, blockade of phosphatidylinositiol 3-kinase (wortmannin) or MAPK pathways with PD 98059 or UO 126 (selective for MAPK kinse 1 and 2) prevented the steroid-induced translocation of Ser-P-ANXA1 to the cell surface. These results suggest that glucocorticoids induce rapid serine phosphorylation and membrane translocation of ANXA1 via a novel nongenomic, glucocorticoid receptor-dependent mechanism that requires MAPK, phosphatidylinositiol 3-kinase, and Ca(2+)-dependent PKC pathways.

Alternative splicing determines sensitivity of murine calcium-activated potassium channels to glucocorticoids

1. Large-conductance Ca(2+)- and voltage-activated potassium (BK) channels are important regulators of cellular excitability. Here, we present a patch-clamp electrophysiological analysis of splice-variant-specific regulation by the synthetic glucocorticoid dexamethasone (DEX) of BK channels consisting of cloned STREX or ZERO alpha-subunit variants expressed in human embryonic kidney (HEK 293) cells. 2. STREX channels in isolated membrane patches were inhibited by protein kinase A (PKA) and this was blocked on pre-treatment of intact cells with DEX (100 nM) for 2 h. 3. The effect of DEX required the synthesis of new mRNA and protein. Furthermore, it required protein phosphatase 2A (PP2A)-like activity intimately associated with the channels, as it was blocked by 10 nM okadaic acid but not by the specific protein phosphatase-1 inhibitor peptide PPI-2. 4. ZERO variant channels that lack the STREX insert were activated by PKA but were not influenced by DEX. ZERO channels containing a mutant STREX domain (S4(STREX)A) were also activated by PKA. Importantly, DEX blocked PKA activation of S4(STREX)A channels in a PP2A-dependent manner. 5. Taken together, the STREX domain is crucial for glucocorticoid regulation of BK channels through a PP2A-type enzyme. Moreover, glucocorticoids appear to induce a generic set of proteins in different types of cells, the actions of which depend on the expression of cell-specific targets.

Hydrogen peroxide attenuates store-operated calcium entry and enhances calcium extrusion in thyroid FRTL-5 cells

Redox modulation participates in the regulation of intracellular free calcium concentration ([Ca(2+)](i)) in several cell types. In thyroid cells, including FRTL-5 cells, changes in [Ca(2+)](i) regulate several important functions, including the production of H(2)O(2) (hydrogen peroxide). As H(2)O(2) is of crucial importance for the production of thyroid hormones, we investigated the effects of H(2)O(2) on [Ca(2+)](i) in thyroid FRTL-5 cells. H(2)O(2) itself did not modulate basal [Ca(2+)](i). However, H(2)O(2) attenuated store-operated calcium entry evoked by thapsigargin, both in a sodium-containing buffer and in a sodium-free buffer. The effect of H(2)O(2) was abrogated by the reducing agent beta-mercaptoethanol. H(2)O(2) also attenuated the thapsigargin-evoked entry of barium and manganese. The effect of H(2)O(2) was, at least in part, mediated by activation of protein kinase C (PKC), as H(2)O(2) enhanced the binding of [(3)H]phorbol 12,13-dibutyrate. H(2)O(2) also stimulated the translocation of the isoenzyme PKCepsilon from the cytosolic fraction to the particulate fraction. Furthermore, H(2)O(2) did not attenuate store-operated calcium entry in cells treated with staurosporine or calphostin C, or in cells with down-regulated PKC. H(2)O(2) depolarized the membrane potential in bisoxonol-loaded cells and when patch-clamp in the whole-cell mode was used. The depolarization was attenuated in cells with down-regulated PKC. This depolarization, at least in part, explained the H(2)O(2)-evoked inhibition of calcium entry. In addition, H(2)O(2) enhanced the extrusion of calcium from cells stimulated with thapsigargin and this effect was abolished in cells with down-regulated PKC and after treatment of the cells with the reducing agent beta-mercaptoethanol. In conclusion H(2)O(2) attenuates an increase in [Ca(2+)](i). As H(2)O(2) is produced in thyroid cells in a calcium-dependent manner, our results suggest that H(2)O(2) may participate in the regulation of [Ca(2+)](i) in these cells via a negative-feedback mechanism involving activation of PKC.

Characterization of hyperpolarization-activated cation currents in mouse anterior pituitary, AtT20 D16:16 corticotropes

The properties of the hyperpolarization-activated inward cation current (Ih) in mouse anterior pituitary, AtT20 D16:16 corticotropes was characterized by whole cell patch clamp recording. In response to hyperpolarizing steps a large, slowly activating, voltage-dependent inward current was activated with a half maximal activation voltage (V0.5) of -96.2+/-3.1 mV with a time constant of 168+/-13 msec determined at -140 mV at room temperature. Ih had a reversal potential of -35.5+/-1.0 mV and -23.3+/-1.4 mV using 5 mM and 25 mM extracellular K+, respectively, with a relative permeability ratio for Na+ and K+ of 0.24. The current was completely blocked by 2 mM extracellular CsCl and partially blocked by ZD7288 (100 microM) but was unaffected by TEA (10 mM) or Ba2+ (1 mM). RT-PCR analysis revealed robust expression of HCN1, but not HCN2 or HCN3, subunits of hyperpolarization-activated cation channels. The endogenous Ih current was weakly activated by cAMP but robustly inhibited by the cAMP antagonist, Rp-8-CPT-cAMPS. Activation or suppression of protein kinase C activity had no significant effect on the Ih current. The data suggest that in AtT20 D16:16 corticotropes Ih is tonically regulated by the cAMP-signaling cascade and may serve to limit excessive hyperpolarization.

Activity of growth factors in the IL-6 group in the differentiation of human lung adenocarcinoma

The role of the interleukin-6 (IL-6) group of cytokines in differentiation of two lung adenocarcinoma cell lines has been examined using induction of alkaline phosphatase and expression of surfactant protein A. Oncostatin M was the most active and potent for alkaline phosphatase in A549 cells, with IL-6 having similar activity but less potency. Neither cytokine induced alkaline phosphatase in NCI-H441 cells, although induction was obtained with lung fibroblast-conditioned medium. Surfactant protein A was induced in NCI-H441 cells by conditioned medium and dexamethasone and, to a much lesser extent, by oncostatin M or IL-6. Induction of alkaline phosphatase and surfactant protein A were both dexamethasone-dependent, though some induction of surfactant protein A was obtained with interferon-alpha in the absence of dexamethasone. The activity present in lung fibroblast-conditioned medium suggests paracrine control, but this appears not to be due to oncostatin M or IL-6 as disabling antibodies to either cytokine were not inhibitory, and, although alkaline phosphatase was induced in A549 by both cytokines, it was only induced by conditioned medium in NCI-H441 cells. Furthermore, surfactant protein A was induced in H441 by conditioned medium to a much greater extent than by oncostatin M or IL-6. These data demonstrate that cytokines of the IL-6 group have potential as differentiation inducers in lung adenocarcinoma cells and that there is an equivalent paracrine factor(s) in lung fibroblast conditioned medium. As the production of this factor by fibroblasts is not enhanced by glucocorticoid, although the response of the target cell is, it would appear to be distinct from the fibrocyte pneumocyte factor previously described by Post et al 1984.

Molecular components of large conductance calcium-activated potassium (BK) channels in mouse pituitary corticotropes

Large-conductance calcium- and voltage- activated potassium (BK) channels play a fundamental role in the signaling pathways regulating mouse anterior pituitary corticotrope function. Here we describe the cloning and functional characterization of the components of mouse corticotrope BK channels. RT-PCR cloning and splice variant analysis of mouse AtT20 D16:16 corticotropes revealed robust expression of mslo transcripts encoding pore-forming alpha-subunits containing the mouse homolog of the 59-amino acid STREX-1 exon at splice site 2. RT-PCR and functional analysis, using the triterpenoid glycoside, DHS-1, revealed that native corticotrope BK channels are not functionally coupled to beta-subunits in vivo. Functional expression of the STREX-1 containing alpha-subunit in HEK 293 cells resulted in BK channels with calcium sensitivity, single-channel conductance, and inhibition by protein kinase A identical to that of native mouse corticotrope BK channels. This report represents the first corticotrope ion channel to be characterized at the molecular level and demonstrates that mouse corticotrope BK channels are composed of alpha-subunits expressing the mouse STREX-1 exon.