18 results on '"David P. McCobb"'
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2. β2 and β4 Subunits of BK Channels Confer Differential Sensitivity to Acute Modulation by Steroid Hormones
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Michael I. Kotlikoff, Jonathan T. King, M. L. Zeeman, Peter V. Lovell, David P. McCobb, and Mark Rishniw
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medicine.medical_specialty ,BK channel ,Patch-Clamp Techniques ,Large-Conductance Calcium-Activated Potassium Channel beta Subunits ,Physiology ,Chromaffin Cells ,medicine.medical_treatment ,Dehydroepiandrosterone ,Gating ,Transfection ,Membrane Potentials ,Steroid ,Rats, Sprague-Dawley ,Internal medicine ,medicine ,Animals ,Humans ,Drug Interactions ,RNA, Messenger ,Cells, Cultured ,Testosterone ,Dose-Response Relationship, Drug ,biology ,Reverse Transcriptase Polymerase Chain Reaction ,Chemistry ,General Neuroscience ,Dose-Response Relationship, Radiation ,Blotting, Northern ,Electric Stimulation ,Potassium channel ,Rats ,Protein Subunits ,Endocrinology ,biology.protein ,Steroids ,Corticosterone ,Glucocorticoid ,medicine.drug ,Hormone - Abstract
Membrane-associated receptors for rapid, steroidal neuromodulation remain elusive. Estradiol has been reported to facilitate activation of voltage- and Ca(2+)-dependent BK potassium channels encoded by Slo, if associated with beta1 subunits. We show here that 1) multiple members of the beta family confer sensitivity to multiple steroids on BK channels, 2) that beta subunits differentiate between steroids, and 3) that different betas have distinct relative preferences for particular steroids. Expressed in HEK 293 cells, inside-out patches with channels composed of Slo-alpha alone showed no steroid sensitivity. Cells expressing alphabeta4 exhibited potent, rapid, reversible, and dose-dependent potentiation by corticosterone (CORT; a glucocorticoid), and were potentiated to a lesser degree by other sex and stress steroids. In contrast, alphabeta2 channels were potentiated more strongly by dehydroepiandrosterone (DHEA; an enigmatic, stress-related adrenal androgen), and to a lesser extent by CORT, estradiol, testosterone, and DHEA-S. Cholesterol had no effect on any BK channel compositions tested. Conductance-voltage plots of channels composed of alpha plus beta2 or beta4 subunits were shifted in the negative direction by steroids, indicating greater activation at negative voltages. Thus our results argue that the variety of Slo-beta subunit coexpression patterns occurring in vivo expands the repertoire of Slo channel gating in yet another dimension not fully appreciated, rendering BK gating responsive to dynamic fluctuations in a multiple of steroid hormones. more...
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- 2006
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3. Acute Modulation of Adrenal Chromaffin Cell BK Channel Gating and Cell Excitability by Glucocorticoids
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David P. McCobb, Jonathan T. King, and Peter V. Lovell
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medicine.medical_specialty ,BK channel ,Patch-Clamp Techniques ,Physiology ,Chromaffin Cells ,Cell ,Gating ,Dexamethasone ,Membrane Potentials ,Potassium Channels, Calcium-Activated ,chemistry.chemical_compound ,Hormone Antagonists ,Species Specificity ,Corticosterone ,Internal medicine ,medicine ,Animals ,Drug Interactions ,Large-Conductance Calcium-Activated Potassium Channels ,Glucocorticoids ,Cells, Cultured ,Dose-Response Relationship, Drug ,biology ,General Neuroscience ,Neural Inhibition ,Electric Stimulation ,Rats ,Mifepristone ,medicine.anatomical_structure ,Endocrinology ,chemistry ,Potassium ,biology.protein ,Calcium ,Cattle ,hormones, hormone substitutes, and hormone antagonists ,Adrenal chromaffin - Abstract
Although adrenal glucocorticoids cortisol and corticosterone (CORT) have numerous “genomic” effects on adrenomedullary chromaffin cells, acute modulatory actions remain largely unknown, despite rapid stress-related changes in secretion. We report that 1 μM glucocorticoids rapidly modulate gating of chromaffin cell BK channels and action potential firing. In general, CORT, or the analog dexamethasone (DEX), increased channel activity in inside-out bovine patches, an effect not blocked by the glucocorticoid receptor (GR) antagonist RU38486. By contrast, these steroids could profoundly inhibit BK activation in many rat patches, while facilitating activation in others. We show that BK inhibition arises from a negative shift in the voltage dependence of BK inactivation paralleling that for activation. We report that rat cells characteristically exhibit greater repetitive firing ability than bovine cells in the absence of glucocorticoids. In both species, steroid application typically increased firing responses to smaller current injections, attributable to BK-enhanced repolarization and Na+ channel deinactivation. However, in rat cells, where BK inactivation is generally faster and more complete, glucocorticoids tended to dampen responses to stronger stimuli. Thus, in the context of natural variation in BK gating, glucocorticoids can either promote or limit firing responses. We suggest that steroids exploit BK gating variety to tailor catecholamine output in a species- and context-specific fashion. more...
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- 2004
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4. Opposing actions of adrenal androgens and glucocorticoids on alternative splicing of Slo potassium channels in bovine chromaffin cells
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Guey-Jen Lai and David P. McCobb
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endocrine system ,medicine.medical_specialty ,Hypophysectomy ,medicine.drug_class ,Chromaffin Cells ,medicine.medical_treatment ,Dehydroepiandrosterone ,Adrenocorticotropic hormone ,Biology ,Dexamethasone ,Potassium Channels, Calcium-Activated ,chemistry.chemical_compound ,Corticosterone ,Internal medicine ,medicine ,Animals ,Large-Conductance Calcium-Activated Potassium Channels ,Glucocorticoids ,Cells, Cultured ,DNA Primers ,Multidisciplinary ,Reverse Transcriptase Polymerase Chain Reaction ,Alternative splicing ,Genetic Variation ,Biological Sciences ,Androgen ,Alternative Splicing ,Kinetics ,Mifepristone ,medicine.anatomical_structure ,Endocrinology ,chemistry ,Adrenal Medulla ,Androgens ,Catecholamine ,Cattle ,Adrenal medulla ,hormones, hormone substitutes, and hormone antagonists ,medicine.drug - Abstract
Pituitary ablation (hypophysectomy) in rats was previously reported to cause a precipitous change in the relative abundance of two alternative splice variants of the “BK”- or “Maxi K”-encoding Slo gene in adrenal chromaffin cells. Inclusion of the optional “STREX” exon (STRess axis-regulated EXon) in a C-terminal splice site was reduced, in preference to the variant lacking an insert at this site. Adrenocorticotropic hormone (ACTH) injections prevented the drop in STREX inclusion, implicating stress-axis function, as opposed to other pituitary functions. Because ACTH promotes synthesis and release of glucocorticoids (corticosterone or cortisol, depending on species), we hypothesized that glucocorticoids applied directly would promote STREX inclusion. Contrary to predictions, we report that direct application of glucocorticoids to bovine cells in vitro decreased STREX inclusion. This effect was blocked by the glucocorticoid receptor antagonist RU38486. As with glucocorticoids, synthesis and release of the adrenal androgen dehydroepiandrosterone (DHEA) increases in response to stress or elevated ACTH levels in some species. We report that direct application of DHEA increased expression of the STREX variant in cultured bovine cells. Two other androgens, androstenedione and testosterone, had similar effects. We hypothesize that Slo splicing in adrenal chromaffin cells in vivo is differentially regulated by the integrative, concentration- and time-dependent actions of glucocorticoids and androgens, with potentially important ramifications for stress-evoked catecholamine secretion. more...
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- 2002
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5. Accurate quantitative RT-PCR for relative expression of Slo splice variants
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Alex L. Bezzerides, Guey-Jen Lai, Yuko Hara, Sahar F. Mahmoud, Peter V. Lovell, David P. McCobb, and Rebecca D. Riba
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Electrophoresis ,DNA, Recombinant ,Computational biology ,Biology ,Nucleic Acid Denaturation ,Potassium Channels, Calcium-Activated ,chemistry.chemical_compound ,Animals ,splice ,Large-Conductance Calcium-Activated Potassium Channels ,Large-Conductance Calcium-Activated Potassium Channel alpha Subunits ,Gene ,Fluorescent Dyes ,Genetics ,Reverse Transcriptase Polymerase Chain Reaction ,General Neuroscience ,Alternative splicing ,Nucleic Acid Heteroduplexes ,Genetic Variation ,Templates, Genetic ,Fluorescence ,Rats ,Real-time polymerase chain reaction ,chemistry ,RNA splicing ,Cattle ,DNA - Abstract
Much interest has been shown in the use of multi-template reverse transcription-polymerase chain reaction (RT-PCR) as a quantitative instrument for low-abundance mRNAs. A desire to achieve finely-graded quantification of the stress- and hormone-related regulation of one splicing decision in an ion channel gene motivated us to test the reliability of simultaneous amplification of two splice variants with one pair of flanking constitutive primers. Unexpectedly indiscriminate heteroduplexing between the two amplification products, despite a large length difference, and their tight comigration with one homoduplex, mandated a rigorously-denaturing electrophoresis protocol. Conveniently, a new fluorescent dye with high affinity for single-stranded DNA has become available. Though the dye has a good dynamic range, we found that dye and gel saturation compounded by the length difference between products introduced an asymmetrical error into the calculation of relative abundance. Avoiding several pitfalls, dye calibration could be used to correct the error. We also found that differences in the amplification efficiency of the two templates were not constant, but dependent on the initial template ratio, requiring a non-linear correction. Together these improvements gave us very consistent quantitative results, and thus advance our analysis of hormonal mechanisms underlying the regulation of alternative splicing of an ion channel critically involved in stress responses. more...
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- 2002
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6. Bovine Versus Rat Adrenal Chromaffin Cells: Big Differences in BK Potassium Channel Properties
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Dustin G. James, David P. McCobb, and Peter V. Lovell
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BK channel ,Patch-Clamp Techniques ,Potassium Channels ,Physiology ,Chromaffin Cells ,Models, Neurological ,chemistry.chemical_element ,In Vitro Techniques ,Calcium ,Membrane Potentials ,Rats, Sprague-Dawley ,Potassium Channels, Calcium-Activated ,Structure-Activity Relationship ,Catecholamines ,Species Specificity ,Adrenal Glands ,Animals ,Large-Conductance Calcium-Activated Potassium Channels ,biology ,Chemistry ,General Neuroscience ,Conductance ,Potassium channel ,Rats ,Kinetics ,biology.protein ,Biophysics ,Cattle ,Ion Channel Gating ,Adrenal chromaffin - Abstract
Both bovine and rat adrenal chromaffin cells have served as pioneering model systems in cellular neurophysiology, including in the study of large conductance calcium- and voltage-dependent K+(BK) channels. We now report that while BK channels dominate the outward current profile of both species, specific gating properties vary widely across cell populations, and the distributions of these properties differ dramatically between species. Although BK channels were first described in bovine chromaffin cells, rapidly inactivating ones were discovered in rat chromaffin cells. We report that bovine cells can also exhibit inactivating BK channels with varying properties similar to those in rat cells. However, a much smaller proportion of bovine cells exhibit inactivating BK current, the proportion of the total current that inactivates is usually smaller, and the rate of inactivation is often much slower. Other gating features differ as well; the voltage dependence of channel activation is much more positive for bovine cells, and their rates of activation and deactivation are faster and slower, respectively. Modeling studies suggest that channel heterogeneity is consistent with varying tetrameric combinations of inactivation-competent versus -incompetent subunits. The results suggest that chromaffin BK channel functional nuances represent an important level for evolutionary tailoring of autonomic stress responses. more...
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- 2000
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7. Control of Alternative Splicing of Potassium Channels by Stress Hormones
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David P. McCobb and Jiuyong Xie
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Male ,medicine.medical_specialty ,Potassium Channels ,Epinephrine ,Chromaffin Cells ,Xenopus ,Molecular Sequence Data ,Peptide hormone ,Biology ,Polymerase Chain Reaction ,Dexamethasone ,Rats, Sprague-Dawley ,Potassium Channels, Calcium-Activated ,Exon ,Adrenocorticotropic Hormone ,Internal medicine ,Gene expression ,medicine ,Animals ,Amino Acid Sequence ,Large-Conductance Calcium-Activated Potassium Channels ,RNA, Messenger ,Large-Conductance Calcium-Activated Potassium Channel alpha Subunits ,Hypophysectomy ,Messenger RNA ,Multidisciplinary ,Phenylethanolamine N-Methyltransferase ,Alternative splicing ,Exons ,biology.organism_classification ,Potassium channel ,Rats ,Alternative Splicing ,medicine.anatomical_structure ,Endocrinology ,Adrenal Medulla ,Oocytes ,Female ,Corticosterone ,Adrenal medulla - Abstract
Many molecular mechanisms for neural adaptation to stress remain unknown. Expression of alternative splice variants of Slo, a gene encoding calcium- and voltage-activated potassium channels, was measured in rat adrenal chromaffin tissue from normal and hypophysectomized animals. Hypophysectomy triggered an abrupt decrease in the proportion of Slo transcripts containing a “STREX” exon. The decrease was prevented by adrenocorticotropic hormone injections. In Xenopus oocytes, STREX variants produced channels with functional properties associated with enhanced repetitive firing. Thus, the hormonal stress axis is likely to control the excitable properties of epinephrine-secreting cells by regulating alternative splicing of Slo messenger RNA. more...
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- 1998
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8. A human calcium-activated potassium channel gene expressed in vascular smooth muscle
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Lawrence Salkoff, James E. Krause, Terence Featherstone, Christopher J. Lingle, Natalie L. Fowler, David P. McCobb, and Mitsuyoshi Saito
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BK channel ,Potassium Channels ,Vascular smooth muscle ,Physiology ,Xenopus ,Molecular Sequence Data ,Gene Expression ,CHO Cells ,Muscle, Smooth, Vascular ,Cricetinae ,Physiology (medical) ,medicine ,Animals ,Humans ,Gene family ,Amino Acid Sequence ,Large-Conductance Calcium-Activated Potassium Channel alpha Subunits ,Base Sequence ,biology ,Chinese hamster ovary cell ,Alternative splicing ,Chromosome Mapping ,Skeletal muscle ,biology.organism_classification ,Calcium-activated potassium channel ,Cell biology ,medicine.anatomical_structure ,Biochemistry ,Molecular Probes ,Oocytes ,biology.protein ,Calcium ,Cardiology and Cardiovascular Medicine - Abstract
Large-conductance Ca(2+)-activated K+ (BK) channels are widespread and functionally heterogeneous. In other classes of K+ channels, functional heterogeneity derives from large gene families, alternative splicing, heterologous subunit composition, and functional modulation. The molecular basis of mammalian BK channel heterogeneity is unknown, since only a single gene (mSlo) has been identified. BK channels in native vascular smooth muscle have an apparent Ca2+ sensitivity approximately 10-fold greater than native brain or skeletal muscle channels, or cloned mSlo channels. Using mSlo as a low-stringency probe, we screened human arterial smooth muscle and genomic libraries extensively in search of genes or splice variants with novel properties. We isolated the human homologue of mSlo, including two novel splice variant forms, but found no other related genes. Electrophysiological characterization of the hSlo clones in Xenopus oocytes and Chinese hamster ovary cells gave BK currents that were not measurably different from mSlo currents. However, coexpression of hSlo with a recently cloned beta-subunit derived from smooth muscle dramatically increased apparent Ca2+ sensitivity. Thus alpha-subunits alone may not determine Ca2+ sensitivity of vascular smooth muscle BK channels. hSlo was mapped to human chromosome 10q23.1, and the genomic structure was analyzed. Immediately after the amino terminal, two unusual regions of trinucleotide repeating sequences are present. The first of these regions encodes polyglycine, and the second encodes polyserine. Both regions of repeated sequence are conserved between the mouse and human genome. more...
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- 1995
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9. Control of hypothalamic-pituitary-adrenal stress axis activity by the intermediate conductance calcium-activated potassium channel, SK4
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Lie Chen, Zhi Liang, Sandra Rizzi, Peter Ruth, Hans-Guenther Knaus, David P. McCobb, Jonathan T. King, Matthias Sausbier, Robert Lukowski, Michael J. Shipston, Heather McClafferty, and Duncan J. MacGregor more...
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Restraint, Physical ,medicine.medical_specialty ,endocrine system ,Hypothalamo-Hypophyseal System ,Physiology ,Molecular and Cellular ,Pituitary-Adrenal System ,Adrenocorticotropic hormone ,Biology ,Membrane Potentials ,03 medical and health sciences ,KCNN4 ,Mice ,0302 clinical medicine ,Anterior pituitary ,Adrenocorticotropic Hormone ,Stress, Physiological ,Transduction, Genetic ,Internal medicine ,medicine ,Animals ,Humans ,RNA, Messenger ,Cells, Cultured ,030304 developmental biology ,Membrane potential ,Mice, Knockout ,0303 health sciences ,Reverse Transcriptase Polymerase Chain Reaction ,Lentivirus ,Depolarization ,Intermediate-Conductance Calcium-Activated Potassium Channels ,Calcium-activated potassium channel ,Potassium channel ,Endocrinology ,medicine.anatomical_structure ,HEK293 Cells ,Female ,Corticotropic cell ,030217 neurology & neurosurgery ,hormones, hormone substitutes, and hormone antagonists - Abstract
Non-technical summary Our ability to respond to stress is critically dependent upon the release of the stress hormone adrenocorticotrophic hormone (ACTH) from corticotroph cells of the anterior pituitary gland. ACTH release is controlled by the electrical properties of corticotrophs that are determined by the movement of ions through channel pores in the plasma membrane. We show that a calcium-activated potassium ion channel called SK4 is expressed in corticotrophs and regulates ACTH release. We provide evidence of how SK4 channels control corticotroph function, which is essential for understanding homeostasis and for treating stress-related disorders. Abstract The anterior pituitary corticotroph is a major control point for the regulation of the hypothalamic–pituitary–adrenal (HPA) axis and the neuroendocrine response to stress. Although corticotrophs are known to be electrically excitable, ion channels controlling the electrical properties of corticotrophs are poorly understood. Here, we exploited a lentiviral transduction system to allow the unequivocal identification of live murine corticotrophs in culture. We demonstrate that corticotrophs display highly heterogeneous spontaneous action-potential firing patterns and their resting membrane potential is modulated by a background sodium conductance. Physiological concentrations of corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) cause a depolarization of corticotrophs, leading to a sustained increase in action potential firing. A major component of the outward potassium conductance was mediated via intermediate conductance calcium-activated (SK4) potassium channels. Inhibition of SK4 channels with TRAM-34 resulted in an increase in corticotroph excitability and exaggerated CRH/AVP-stimulated ACTH secretion in vitro. In accordance with a physiological role for SK4 channels in vivo, restraint stress-induced plasma ACTH and corticosterone concentrations were significantly enhanced in gene-targeted mice lacking SK4 channels (Kcnn4−/−). In addition, Kcnn4−/− mutant mice displayed enhanced hypothalamic c-fos and nur77 mRNA expression following restraint, suggesting increased neuronal activation. Thus, stress hyperresponsiveness observed in Kcnn4−/− mice results from enhanced secretagogue-induced ACTH output from anterior pituitary corticotrophs and may also involve increased hypothalamic drive, thereby suggesting an important role for SK4 channels in HPA axis function. more...
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- 2011
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10. Action potential waveform voltage-clamp commands reveal striking differences in calcium entry via low and high voltage activated calcium channels
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David P. McCobb and Kurt G. Beam
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Neurons ,Voltage-dependent calcium channel ,General Neuroscience ,Voltage clamp ,Action Potentials ,chemistry.chemical_element ,Chick Embryo ,Gating ,Calcium ,Calcium in biology ,Kinetics ,Electrophysiology ,chemistry ,Ganglia, Spinal ,Biophysics ,Animals ,Calcium Channels ,Patch clamp ,Neuroscience ,Transduction (physiology) - Abstract
Calcium channels transduce natural voltage transients, like action potentials, into functionally important intracellular calcium transients. We have used digitally constructed waveforms that simulate natural action potentials as voltage-clamp commands to study channel function in transduction. Whole-cell calcium currents elicited by several action potential waveforms (APWs) were studied. The currents were subdivided into T (or low voltage-activated) and high voltage-activated components. Calcium entry through T channels constituted a disproportionately large fraction of the total during normal, brief APWs. Entry through high voltage-activated channels was much more responsive to APW, increasing more significantly as APW duration increased. Thus the results indicate that differences in the gating properties of these two channel classes combine to endow them with strikingly different transducer properties. more...
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- 1991
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11. The differentiation of excitability in embryonic chick limb motoneurons
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PM Best, David P. McCobb, and Kurt G. Beam
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Potassium Channels ,Action Potentials ,Chick Embryo ,Tetrodotoxin ,Hindlimb ,Biology ,Sodium Channels ,Neuromuscular junction ,chemistry.chemical_compound ,medicine ,Animals ,Patch clamp ,4-Aminopyridine ,Motor Neurons ,Muscles ,General Neuroscience ,Sodium channel ,Electric Conductivity ,Tetraethylammonium ,Extremities ,Articles ,Tetraethylammonium Compounds ,Motor neuron ,Electrophysiology ,medicine.anatomical_structure ,nervous system ,chemistry ,embryonic structures ,Forelimb ,Neuroscience - Abstract
The well-documented role of neuromuscular activity as a regulator of motoneuron and muscle development raises important questions about the differentiation of excitability in motoneurons. We have recently described changes in expression of voltage-dependent calcium currents that take place during neuromuscular development in the chick embryo (McCobb et al., 1989). We now report similar analyses, using whole-cell patch-recording methods, of the major currents underlying action potential generation in the same motoneurons. Studies were conducted on identified hindlimb motoneurons isolated from the spinal cord at 3 very different stages of chick hindlimb development. Motoneurons could generate overshooting action potentials at the earliest stage studied [embryonic day 4 (E4)]. However, large changes in densities of several voltage-dependent ionic currents occurred thereafter. E6 and E11 motoneurons had progressively larger INa densities and, consequently, greater action potential amplitudes. Densities of 2 potassium currents, Ik and IA, increased on separate schedules. The relatively late and much larger increase in IA resulted in a substantial developmental decline in action potential duration. These changes, which will greatly affect motoneuron output to muscle by affecting Ca2+ entry through voltage-gated channels, occur at the same time that activity-dependent developmental changes occur in the neuromuscular system. more...
- Published
- 1990
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12. Regulation of alternative splicing of Slo K+ channels in adrenal and pituitary during the stress-hyporesponsive period of rat development
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Guey-Jen Lai and David P. McCobb
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Male ,endocrine system ,medicine.medical_specialty ,Pituitary gland ,Hydrocortisone ,Chromaffin Cells ,Biology ,Rats, Sprague-Dawley ,chemistry.chemical_compound ,Endocrinology ,Receptors, Glucocorticoid ,Anterior pituitary ,Corticosterone ,Pituitary Gland, Anterior ,Stress, Physiological ,Internal medicine ,Testis ,medicine ,Animals ,Testosterone ,Large-Conductance Calcium-Activated Potassium Channels ,Large-Conductance Calcium-Activated Potassium Channel alpha Subunits ,Cells, Cultured ,Hypophysectomy ,Adrenal cortex ,Alternative splicing ,Gene Expression Regulation, Developmental ,Protein Structure, Tertiary ,Rats ,Alternative Splicing ,medicine.anatomical_structure ,Epinephrine ,Receptors, Mineralocorticoid ,chemistry ,Adrenal Medulla ,Adrenal medulla ,hormones, hormone substitutes, and hormone antagonists ,Endocrine gland ,medicine.drug - Abstract
Stress triggers release of ACTH from the pituitary, glucocorticoids from the adrenal cortex, and epinephrine from the adrenal medulla. Although functions differ, these hormone systems interact in many ways. Previous evidence indicates that pituitary and steroid hormones regulate alternative splicing of the Slo gene at the stress axis-regulated exon (STREX), with functional implications for the calcium-activated K+ channels prominent in adrenal medullary and pituitary cells. Here we examine the role of corticosterone in Slo splicing regulation in pituitary and adrenal tissues during the stress-hyporesponsive period of early rat postnatal life. The sharp drop in plasma corticosterone (CORT) that defines this period offers a unique opportunity to test CORT's role in Slo splicing. We report that in both adrenal and pituitary tissues, the percentage of Slo transcripts having STREX declines and recovers in parallel with CORT. Moreover, addition of 500 nm CORT to cultures of anterior pituitary cells from 13-, 21-, and 30-d postnatal animals increased the percentage of Slo transcripts with STREX, whereas 20 microm CORT reduced STREX representation. Applied to adrenal chromaffin cells, 20 microm CORT decreased STREX inclusion, whereas neither 500 nm nor 2 microm had any effect. The mineralocorticoid receptor antagonist RU28318 abolished the effect of 500 nm CORT on splicing in pituitary cells, whereas the glucocorticoid receptor antagonist RU38486 blocked the effect of 20 microm CORT on adrenal chromaffin cells. These results support the hypothesis that the abrupt, transient drop in CORT during the stress-hyporesponsive period drives the transient decline in STREX splice variant representation in pituitary, but not adrenal. more...
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- 2006
13. Towards a natural history of calcium-activated potassium channels
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David P. McCobb
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SK channel ,BK channel ,Bursting ,chemistry ,biology ,biology.protein ,T-type calcium channel ,chemistry.chemical_element ,Gating ,Calcium ,Neuroscience ,Calcium-activated potassium channel ,Potassium channel - Abstract
Publisher Summary This chapter focuses on calcium-activated potassium channels (K Ca ). K Ca channels have provided strategic advantages for many cells. Those with and without additional voltage dependence are co-deployed in many cases. All probably participate in negative-feedback protection against calcium overload in some contexts; however, they have many other roles, some even contradictory to this role. Slo gene-encoded BK channels dampen excitation, secretion, and contraction, facilitate rapid spiking and secretion, enhance auditory frequency discrimination, modulate presynaptic output, shape rhythmicity, and transport potassium in bulk. Barely studied paralogs of Slo (Slo2, Slack, and Slo3) have mysterious chloride-, calcium-, or pH-sensitive aspects to their gating. SK channels from several genes mediate spike frequency adaptation, help pace rhythmic bursting, prevent rhythmic bursting, fine-tune threshold, and influence wakefulness and memory formation. Related IK channels provide a driving force for calcium and help regulate immune function and hematopoiesis. Some of the classically described K Ca channels—for example, those that help regulate ciliary beating in Paramecium and those that produce the quiet phase in elegant molluscan bursting rhythms—remain uncharacterized at the molecular level. more...
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- 2004
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14. Subordination stress alters alternative splicing of the Slo gene in tree shrew adrenals
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Guey-Jen Lai, David P. McCobb, Gabriele Flügge, Yuko Hara, and Sahar F. Mahmoud
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Dominance-Subordination ,Male ,medicine.medical_specialty ,BK channel ,Hypothalamo-Hypophyseal System ,Hydrocortisone ,Behavioral Neuroscience ,Exon ,Potassium Channels, Calcium-Activated ,Endocrinology ,Internal medicine ,Adrenal Glands ,medicine ,Sympathoadrenal system ,Animals ,Chronic stress ,Large-Conductance Calcium-Activated Potassium Channels ,Hypophysectomy ,Sex Characteristics ,biology ,Endocrine and Autonomic Systems ,Alternative splicing ,Body Weight ,Tupaiidae ,Organ Size ,Sexual dimorphism ,Alternative Splicing ,medicine.anatomical_structure ,Chromaffin cell ,biology.protein ,Female ,Stress, Psychological ,Hormone - Abstract
It was previously hypothesized that stress hormones regulate the alternative splicing of Slo potassium channels, thereby tuning the intrinsic excitability of adrenal chromaffin cells. Male tree shrews subjected to chronic stress by exposure to a dominant male develop robust symptoms with parallels to human depression. We report here that adrenals from males subjected to 4-6 weeks of subordination have a significantly smaller proportion of Slo transcripts with the optional STREX exon (STRess-axis regulated EXon) than unstressed male adrenals. Female adrenals (unstressed) had even lower levels than stressed males. These data suggest both behavioral regulation and sexual dimorphism in ion channel structure. We hypothesize that chromaffin cell excitability and sympathoadrenal function will be altered, and speculate that this may favor passive coping responses in subordinate males and females. more...
- Published
- 2003
15. Pituitary control of BK potassium channel function and intrinsic firing properties of adrenal chromaffin cells
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Peter V. Lovell and David P. McCobb
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BK channel ,medicine.medical_specialty ,endocrine system ,Hypophysectomy ,Patch-Clamp Techniques ,Potassium Channels ,medicine.medical_treatment ,Chromaffin Cells ,Action Potentials ,Gating ,Models, Biological ,Rats, Sprague-Dawley ,Potassium Channels, Calcium-Activated ,Internal medicine ,medicine ,Endocrine system ,Animals ,Computer Simulation ,Patch clamp ,Large-Conductance Calcium-Activated Potassium Channels ,ARTICLE ,Large-Conductance Calcium-Activated Potassium Channel alpha Subunits ,Cells, Cultured ,biology ,Chemistry ,General Neuroscience ,Depolarization ,Potassium channel ,Electric Stimulation ,Rats ,Alternative Splicing ,Pituitary Hormones ,Endocrinology ,Pituitary Gland ,biology.protein ,Biophysics ,Catecholamine ,Ion Channel Gating ,medicine.drug - Abstract
The discovery that the hypothalamic–pituitary–adrenocortical (HPA) endocrine stress axis controls an alternative splicing decision in chromaffinSlo-encoded BK (big potassium) channels raised the possibility that activation of the HPA could serve as a mechanism to tune the intrinsic electrical properties of epinephrine-secreting adrenal chromaffin cells. To test this, we compared BK functional properties and cell excitability in chromaffin cells from normal and hypophysectomized (pituitary-ablated) rats. Hypophysectomy was found to alter the voltage dependence and kinetics of BK gating, making channels less accessible for activation from rest. Perforated-patch recordings revealed changes in action potential waveform and repetitive firing properties. The maximum number of spikes that could be elicited with a 2 sec depolarizing current pulse was reduced by ∼50% by hypophysectomy. The results indicate that pituitary hormones can adapt the mechanics of adrenal catecholamine release by tailoring BK channel function. more...
- Published
- 2001
16. mSlo, a complex mouse gene encoding 'maxi' calcium-activated potassium channels
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Lawrence Salkoff, Alice Butler, Aguan Wei, Susan Tsunoda, and David P. McCobb
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BK channel ,Potassium Channels ,Charybdotoxin ,Transcription, Genetic ,Potassium ,Xenopus ,Molecular Sequence Data ,chemistry.chemical_element ,Scorpion Venoms ,RNA, Complementary ,chemistry.chemical_compound ,KCNN4 ,Mice ,Potassium Channels, Calcium-Activated ,Animals ,Amino Acid Sequence ,Large-Conductance Calcium-Activated Potassium Channels ,Genetics ,Multidisciplinary ,biology ,Sodium ,Electric Conductivity ,Membrane Proteins ,Tetraethylammonium ,DNA ,Iberiotoxin ,Tetraethylammonium Compounds ,biology.organism_classification ,Potassium channel ,Calcium-activated potassium channel ,Cell biology ,Alternative Splicing ,chemistry ,biology.protein ,Oocytes ,RNA ,Calcium ,Drosophila ,Peptides - Abstract
Complementary DNAs (cDNAs) from mSlo, a gene encoding calcium-activated potassium channels, were isolated from mouse brain and skeletal muscle, sequenced, and expressed in Xenopus oocytes. The mSlo-encoded channel resembled "maxi" or BK (high conductance) channel types; single channel conductance was 272 picosiemens with symmetrical potassium concentrations. Whole cell and single channel currents were blocked by charybdotoxin, iberiotoxin, and tetraethylammonium ion. A large number of variant mSlo cDNAs were isolated, indicating that several diverse mammalian BK channel types are produced by a single gene. more...
- Published
- 1993
17. The genesis of membrane bone in the embryonic chick maxilla: epithelial-mesenchymal tissue recombination studies
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Mary S. Tyler and David P. McCobb
- Subjects
animal structures ,Molecular Biology ,Developmental Biology - Abstract
In the present study, the question of whether a relatively non-specific epithelial requirement exists for membrane bone formation within the maxillary mesenchyme was investigated. Organ rudiments from embryonic chicks of three to five days of incubation (HH .18 –25) were enzymatically separated into the epithelial and mesenchymal components. Maxillary mesenchyme (from embryos HH 18 –19) which in the absence of epithelium will not form bone was recombined with epithelium from maxillae of similarly aged embryos (homotypic-homochronic recombination) and of older embryos (HH 25) (homotypic-heterochronic recombination). Heterotypic recombinations were made between maxillary mesenchyme (HH 18 –19) and the epithelium from wing and hind-limb buds (HH 19 –22). Recombinants were grown as grafts on the chorioallantoic membranes of host chick embryos. Grafts of intact maxillae, isolated maxillary mesenchyme, and isolated epithelia from the maxilla, wing-, and hind-limb buds were grown as controls. The histodifferentiation of grafted intact maxillae was similar to that in vivo; both cartilage and membrane bone differentiated within the mesenchyme. Grafts of maxillary mesenchyme (from embryos HH 18 –19) grown in the absence of epithelium formed cartilage but did not form membrane bone. Grafts of maxillary mesenchyme (from embryos HH 18 –19) recombined with epithelium in homotypic-homochronic, homotypic-heterochronic, and heterotypic tissue combinations formed membrane bone in addition to cartilage. These results indicate that maxillary mesenchyme requires the presence of epithelium to promote osteogenesis and that this epithelial requirement is relatively non-specific in terms of type and age of epithelium. more...
- Published
- 1980
- Full Text
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18. Development alters the expression of calcium currents in chick limb motoneurons
- Author
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David P. McCobb, Kurt G. Beam, and Phillip M. Best
- Subjects
chemistry.chemical_element ,Action Potentials ,Chick Embryo ,Calcium current ,Biology ,Calcium ,Amiloride ,Embryonic and Fetal Development ,In vivo ,Animals ,Voltage dependence ,Cells, Cultured ,Calcium metabolism ,Motor Neurons ,System development ,General Neuroscience ,Embryo ,Cell biology ,Hindlimb ,nervous system ,chemistry ,Verapamil ,embryonic structures ,Calcium Channels ,Neuroscience ,Ion Channel Gating - Abstract
Calcium current types expressed in vertebrate spinal motoneurons have not been previously resolved. We have resolved three types in chick limb motoneurons identified by retrograde labeling and report that dramatic changes in their expression take place during development in vivo. T-, N-, and L-type calcium currents were distinguished on the basis of kinetics, voltage dependence, and unique pharmacological sensitivities. Developmental changes were characterized by studying motoneurons isolated from embryos at three stages spanning neuromuscular system development. T currents were dominant at the earliest stage. Motoneurons from embryos 2 days older showed much reduced T currents and much increased N and L currents. We suggest that mature motoneurons will be dominated by N- and L-type calcium currents and that T current may serve developmental roles. more...
- Published
- 1989
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