scholarly journals SLO2.1 and NALCN form a functional complex to modulate myometrial cell excitability

2020 ◽  
Author(s):  
Juan J. Ferreira ◽  
Chinwendu Amazu ◽  
Lis C. Puga-Molina ◽  
Sarah K. England ◽  
Celia M. Santi
Keyword(s):  
Membrane Potential ◽  
Resting Membrane Potential ◽  
Quiescent State ◽  
Leak Current ◽  
Contractile State ◽  
Cell Excitability ◽  
Leak Channel ◽  
Functional Complex ◽  
Myometrial Smooth Muscle Cell ◽  
Myometrial Contractility

AbstractAt the end of pregnancy, the uterus transitions from a quiescent state to an excitable, contractile state. These changes are linked to depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential. The membrane potential is primarily determined by the balance between an outward potassium (K+) leak current and an inward sodium (Na+) leak current. We recently described a Na+-activated K+ channel (SLO2.1) and a non-selective Na+ leak channel (NALCN) in human MSMCs. Here, we asked whether these channels function together. We show that SLO2.1 currents are activated by an inward NALCN-dependent Na+ leak current, leading to MSMC hyperpolarization. The regulation of the membrane potential by NALCN/SLO2.1 activity modulates both Ca2+ entry through VDCCs, and myometrial contractility. Finally, NALCN and SLO2.1 are in proximity to one another in human MSMCs. We conclude that SLO2.1 and NALCN function together to regulate human MSMC membrane potential and excitability.

scholarly journals Progesterone and estrogen regulate NALCN expression in human myometrial smooth muscle cells

2020 ◽  
Vol 318 (4) ◽  
pp. E441-E452 ◽  
Author(s):  
Chinwendu Amazu ◽  
Xiaofeng Ma ◽  
Clara Henkes ◽  
Juan J. Ferreira ◽  
Celia M. Santi ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Microarray Data ◽  
Quiescent State ◽  
Leak Current ◽  
Response Elements ◽  
Contractile State ◽  
Leak Channel ◽  
Estrogen Response ◽  
Myometrial Smooth Muscle Cell ◽  
Dysfunctional Labor

During pregnancy, the uterus transitions from a quiescent state to an excitable, highly contractile state to deliver the fetus. Two important contributors essential for this transition are hormones and ion channels, both of which modulate myometrial smooth muscle cell (MSMC) excitability. Recently, the sodium (Na+) leak channel, nonselective (NALCN), was shown to contribute to a Na+ leak current in human MSMCs, and mice lacking NALCN in the uterus had dysfunctional labor. Microarray data suggested that the proquiescent hormone progesterone (P4) and the procontractile hormone estrogen (E2) regulated this channel. Here, we sought to determine whether P4 and E2 directly regulate NALCN. In human MSMCs, we found that NALCN mRNA expression decreased by 2.3-fold in the presence of E2 and increased by 5.6-fold in the presence of P4. Similarly, E2 treatment decreased, and P4 treatment restored NALCN protein expression. Additionally, E2 significantly inhibited, and P4 significantly enhanced an NALCN-dependent leak current in MSMCs. Finally, we identified estrogen response and progesterone response elements (EREs and PREs) in the NALCN promoter. With the use of luciferase assays, we showed that the PREs, but not the ERE, contributed to regulation of NALCN expression. Our findings reveal a new mechanism by which NALCN is regulated in the myometrium and suggest a novel role for NALCN in pregnancy.

scholarly journals The sodium leak channel NALCN encodes the major background sodium ion conductance in murine anterior pituitary cells

2021 ◽  
Author(s):  
Marziyeh Belal ◽  
Mariusz Mucha ◽  
Arnaud Monteil ◽  
Paul G Winyard ◽  
Robert Pawlak ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Pituitary Cell ◽  
Resting Membrane Potential ◽  
Pituitary Cells ◽  
Firing Activity ◽  
Cell Excitability ◽  
Leak Channel ◽  
Anterior Pituitary Cells

The pituitary gland, the so-called master gland produces and secretes a variety of hormones essential for regulating growth and development, metabolic homeostasis, reproduction, and the stress response. The interplay between the brain and peripheral feedback signals controls hormone secretion from pituitary cells by regulating the properties of ion channels, and in turn, cell excitability. Endocrine anterior pituitary cells fire spontaneous action potentials to regulate their intracellular calcium level and eventually hormone secretion. However, the molecular identity of the non-selective cationic leak channel involved in maintaining the resting membrane potential at the firing threshold remained unknown. Here, we show that the sodium leak channel NALCN, known to modulate neuronal excitability, also regulates excitability in murine anterior pituitary cells. Using viral transduction combined with electrophysiology and calcium imaging we show that NALCN encodes the major Na+ leak conductance which tunes the resting membrane potential close to firing threshold to sustain the intrinsically-regulated firing in endocrine pituitary cells. Genetic interruption of NALCN channel activity, hyperpolarised the membrane potential drastically and stopped the firing activity, and consequently abolished the cytosolic calcium oscillations. Moreover, we found that NALCN conductance forms a very small fraction of the total cell conductance yet has a profound impact on modulating pituitary cell excitability. Taken together, our results demonstrate that, NALCN is a crucial regulator of pituitary cell excitability and supports spontaneous firing activity to consequently regulate hormonal secretion. Our results suggest that receptor-mediated and potentially circadian changes in NALCN conductance can powerfully affect the pituitary activity and hormone secretion.

scholarly journals Leak Current Rectification in Myxicola Giant Axons

1969 ◽  
Vol 54 (6) ◽  
pp. 755-764 ◽  
Author(s):  
L. Goldman ◽  
L. Binstock
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Resting Membrane Potential ◽  
Constant Field ◽  
Leak Current ◽  
Giant Axons ◽  
Time To Peak ◽  
Zero Current ◽  
Current Voltage ◽  
Current Voltage Curve

Early leak current, i.e. for times similar to the time to peak of the transient current was measured in Myxicola giant axons in the presence of tetrodotoxin. The leak current-voltage relation rectifies, showing more current for strong depolarizing pulses than expected from symmetry around the holding potential. A satisfactory practical approximation for most leak corrections is constant resting conductance. The leak current-voltage curve rectifies less than expected from the constant field equation. These curves cannot be reconstructed by summing the constant field currents for sodium and potassium using a PNa/PK ratio obtained in the usual way, from zero current constant field fits to resting membrane potential data. Nor can they be reconstructed by summing the constant field current for potassium with that for any other single ion. They can be reconstructed, however, by summing the constant field current for potassium with a constant conductance component. It is concluded that the leak current and the resting membrane potential, therefore, are determined by multiple ionic components, at least three and possibly many. Arguments are presented suggesting that ion permeability ratios obtained in the usual way, by fitting the constant field equation to resting membrane potential data should be viewed with skepticism.

Effect of low chloride on relaxation in hamster diaphragm muscle

1986 ◽  
Vol 61 (1) ◽  
pp. 180-184 ◽  
Author(s):  
S. A. Esau ◽  
N. Sperelakis
Keyword(s):  
Membrane Potential ◽  
Muscle Fatigue ◽  
Time Constant ◽  
Diaphragm Muscle ◽  
Resting Membrane Potential ◽  
Krebs Solution ◽  
Sarcolemmal Membrane ◽  
Cl Conductance

With muscle fatigue the chloride (Cl-) conductance of the sarcolemmal membrane decreases. The role of lowered Cl- conductance in the prolongation of relaxation seen with fatigue was studied in isolated hamster diaphragm strips. The muscles were studied in either a Krebs solution or a low Cl- solution in which half of the NaCl was replaced by Na-gluconate. Short tetanic contractions were produced by a 160-ms train of 0.2-ms pulses at 60 Hz from which tension (T) and the time constant of relaxation were measured. Resting membrane potential (Em) was measured using KCl-filled microelectrodes with resistances of 15–20 M omega. Mild fatigue (20% fall in tension) was induced by 24–25 tetanic contractions at the rate of 2/s. There was no difference in Em or T in the two solutions, either initially or with fatigue. The time constant of relaxation was greater in low Cl- solution, both initially (22 +/- 3 vs. 18 +/- 5 ms, mean +/- SD, P less than 0.05) and with fatigue (51 +/- 18 vs. 26 +/- 7 ms, P less than 0.005). Lowering of sarcolemmal membrane Cl- conductance appears to play a role in the slowing of relaxation of hamster diaphragm muscle seen with fatigue.

Calcium channels and excitation–contraction coupling in cardiac cells. I. Two components of contraction in guinea-pig papillary muscle

1987 ◽  
Vol 65 (9) ◽  
pp. 1821-1831 ◽  
Author(s):  
E. Honoré ◽  
M. M. Adamantidis ◽  
B. A. Dupuis ◽  
C. E. Challice ◽  
P. Guilbault
Keyword(s):  
Membrane Potential ◽  
Guinea Pig ◽  
Papillary Muscle ◽  
Cardiac Cells ◽  
Resting Membrane Potential ◽  
Tonic Component ◽  
Contraction Coupling ◽  
Rich Solution ◽  
The Relationship ◽  
Guinea Pig Atria

Biphasic contractions have been obtained in guinea-pig papillary muscle by inducing partial depolarization in K+-rich solution (17 mM) containing 0.3 μM isoproterenol; whereas in guinea-pig atria, the same conditions led to monophasic contractions corresponding to the first component of contraction in papillary muscle. The relationships between the amplitude of the two components of the biphasic contraction and the resting membrane potential were sigmoidal curves. The first component of contraction was inactivated for membrane potentials less positive than those for the second component. In Na+-low solution (25 mM), biphasic contraction became monophasic subsequent to the loss of the second component, but tetraethylammonium unmasked the second component of contraction. The relationship between the amplitude of the first component of contraction and the logarithm of extracellular Ca2+ concentration was complex, whereas for the second component it was linear. When Ca2+ ions were replaced by Sr2+ ions, only the second component of contraction was observed. It is suggested that the first component of contraction may be triggered by a Ca2+ release from sarcoplasmic reticulum, induced by the fast inward Ca2+ current and (or) by the depolarization. The second component of contraction may be due to a direct activation of contractile proteins by Ca2+ entering the cell along with the slow inward Ca2+ current and diffusing through the sarcoplasm. These results do not exclude the existence of a third "tonic" component, which could possibly be mixed with the second component of contraction.

scholarly journals Activation of Ca(2+)-dependent K+ current by acetylcholine and histamine in a human gastric epithelial cell line.

1993 ◽  
Vol 102 (4) ◽  
pp. 667-692 ◽  
Author(s):  
E Hamada ◽  
T Nakajima ◽  
S Ota ◽  
A Terano ◽  
M Omata ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Epithelial Cell ◽  
Cell Line ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Induced Response ◽  
Epithelial Cell Line ◽  
Bathing Solution ◽  
Pipette Solution ◽  
K Current

The effects of acetylcholine (ACh) and histamine (His) on the membrane potential and current were examined in JR-1 cells, a mucin-producing epithelial cell line derived from human gastric signet ring cell carcinoma. The tight-seal, whole cell clamp technique was used. The resting membrane potential, the input resistance, and the capacitance of the cells were approximately -12 mV, 1.4 G ohms, and 50 pF, respectively. Under the voltage-clamp condition, no voltage-dependent currents were evoked. ACh or His added to the bathing solution hyperpolarized the membrane by activating a time- and voltage-independent K+ current. The ACh-induced hyperpolarization and K+ current persisted, while the His response desensitized quickly (< 1 min). These effects of ACh and His were mediated predominantly by m3-muscarinic and H1-His receptors, respectively. The K+ current induced by ACh and His was inhibited by charybdotoxin, suggesting that it is a Ca(2+)-activated K+ channel current (IK.Ca). The measurement of intracellular Ca2+ ([Ca2+]i) using Indo-1 revealed that both agents increased [Ca2+]i with similar time courses as they increased IK.Ca. When EGTA in the pipette solution was increased from 0.15 to 10 mM, the induction of IK.Ca by ACh and His was abolished. Thus, both ACh and His activate IK.Ca by increasing [Ca2+]i in JR-1 cells. In the Ca(2+)-free bathing solution (0.15 mM EGTA in the pipette), ACh evoked IK.Ca transiently. Addition of Ca2+ (1.8 mM) to the bath immediately restored the sustained IK.Ca. These results suggest that the ACh response is due to at least two different mechanisms; i.e., the Ca2+ release-related initial transient activation and the Ca2+ influx-related sustained activation of IK.Ca. Probably because of desensitization, the Ca2+ influx-related component of the His response could not be identified. Intracellularly applied inositol 1,4,5-trisphosphate (IP3), with and without inositol 1,3,4,5-tetrakisphosphate (IP4), mimicked the ACh response. IP4 alone did not affect the membrane current. Under the steady effect of IP3 or IP3 plus IP4, neither ACh nor His further evoked IK.Ca. Intracellular application of heparin or of the monoclonal antibody against the IP3 receptor, mAb18A10, inhibited the ACh and His responses in a concentration-dependent fashion. Neomycin, a phospholipase C (PLC) inhibitor, also inhibited the agonist-induced response in a concentration-dependent fashion. Although neither pertussis toxin (PTX) nor N-ethylmaleimide affected the ACh or His activation of IK,Ca, GDP beta S attenuated and GTP gamma S enhanced the agonist response.(ABSTRACT TRUNCATED AT 400 WORDS)

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