BK channel β1-subunit regulation of calcium handling and constriction in tracheal smooth muscle

The large-conductance, Ca2+-activated K+ (BK) channels are regulators of voltage-dependent Ca2+ entry in many cell types. The BK channel accessory β1-subunit promotes channel activation in smooth muscle and is required for proper tone in the vasculature and bladder. However, although BK channels have also been implicated in airway smooth muscle function, their regulation by the β1-subunit has not been investigated. Utilizing the gene-targeted mice for the β1-subunit gene, we have investigated the role of the β1-subunit in tracheal smooth muscle. In mice with the β1-subunit-knockout allele, BK channel activity was significantly reduced in excised tracheal smooth muscle patches and spontaneous BK currents were reduced in whole tracheal smooth muscle cells. Knockout of the β1-subunit resulted in an increase in resting Ca2+ levels and an increase in the sustained component of Ca2+ influx after cholinergic signaling. Tracheal constriction studies demonstrate that the level of constriction is the same with knockout of the β1-subunit and BK channel block with paxillin, indicating that BK channels contribute little to airway relaxation in the absence of the β1-subunit. Utilizing nifedipine, we found that the increased constriction caused by knockout of the β1-subunit could be accounted for by an increased recruitment of L-type voltage-dependent Ca2+ channels. These results indicate that the β1-subunit is required in airway smooth muscle for control of voltage-dependent Ca2+ influx during rest and after cholinergic signaling in BK channels.

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Expression of dihydropyridine resistance differs in porcine bronchial and tracheal smooth muscle

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1994.267.2.l106 ◽

1994 ◽

Vol 267 (2) ◽

pp. L106-L112 ◽

Cited By ~ 2

Author(s):

T. L. Croxton ◽

C. Fleming ◽

C. A. Hirshman

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Isometric Tension ◽

Tracheal Smooth Muscle ◽

Airway Smooth Muscle Cells ◽

Channel Blockers ◽

Response Curves ◽

Voltage Dependent ◽

Relaxation Responses ◽

Ca2 Channels

Voltage-dependent and receptor-operated Ca2+ entry mechanisms have been demonstrated in airway smooth muscle, but their relative importance for maintenance of contraction is unknown. Blockade of voltage-dependent Ca2+ channels (VDC) has produced inconsistent relaxation. We postulated regional variations in Ca2+ handling by airway smooth muscle cells and compared the efficacy of dihydropyridine VDC blockers in tracheas and bronchi. Porcine tracheal smooth muscle strips and bronchial rings were mounted in tissue baths filled with physiological solutions and isometric tension was measured. Tissues were precontracted with carbachol or KCl, and relaxation dose-response curves to nifedipine, Mn2+, or Cd2+ were obtained. Relaxation responses to nifedipine were significantly different in carbachol-contracted tracheas and bronchi. Whereas carbachol-contracted tracheal muscle completely relaxed with 10(-6) M nifedipine, bronchial smooth muscle relaxed < 50%. In contrast, KCl-contracted bronchial muscle was completely relaxed by nifedipine. The nonspecific Ca2+ channel blockers Mn2+ and Cd2+ produced similar relaxation responses in each tissue. Thus VDC are the predominant mechanism for Ca2+ entry in porcine tracheal smooth muscle, but a dihydropyridine-insensitive pathway is functionally important in carbachol-contracted porcine bronchi. Regional variation may account for apparent inconsistencies between previous studies.

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Calcium Handling in Airway Smooth Muscle: Mechanisms and Therapeutic Implications

Canadian Respiratory Journal ◽

10.1155/1998/678027 ◽

1998 ◽

Vol 5 (6) ◽

pp. 491-498 ◽

Cited By ~ 9

Author(s):

Luke J Janssen

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Calcium Handling ◽

Muscle Physiology ◽

Therapeutic Implications ◽

Cellular Processes ◽

Voltage Dependent ◽

Complicated Model ◽

Voltage Dependent Calcium Channels ◽

Internal Calcium

Calcium plays a central role in the activation of many cellular processes, including the most relevant end-point in airway smooth muscle physiology: contraction. For this reason, the cytosolic concentration of calcium is tightly controlled by an elaborate array of mechanisms. The latter include multiple entry pathways from the extracellular space, a pump on the membrane that extrudes calcium out of the cell, an internal pump that sequesters calcium into an intracellular pool and at least two types of release sites from which sequestered calcium can be released back into the cytosol; all of these mechanisms are tightly regulated by second messenger-signalling pathways. Understanding of the relationship between calcium handling and contraction ("excitation-contraction coupling") has progressed from a mechanism in which activation of voltage-dependent calcium channels plays a central role (as in skeletal muscle) to a mechanism in which a small localized signalling event triggers a massive release of internal calcium (as in cardiac muscle) to a more complicated model in which the internal calcium pool divides the cytosol into two physiologically distinct spaces where the cytosolic concentration of calcium is regulated independently (as in vascular smooth muscle). The changes that may occur in calcium-handling pathways in asthma and the opportunities for novel approaches to the treatment of asthma are also discussed.

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Chloroform Extract ofArtemisia annuaL. Relaxes Mouse Airway Smooth Muscle

Evidence-based Complementary and Alternative Medicine ◽

10.1155/2017/9870414 ◽

2017 ◽

Vol 2017 ◽

pp. 1-12 ◽

Cited By ~ 3

Author(s):

Jun Huang ◽

Li-Qun Ma ◽

Yongle Yang ◽

Nana Wen ◽

Wan Zhou ◽

...

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Single Channel ◽

Artemisia Annua ◽

Chloroform Extract ◽

Bk Channels ◽

Bk Channel ◽

Airway Smooth Muscle Cells ◽

Patch Clamp Technique ◽

Channel Currents

Artemisia annuaL. belongs to the Asteraceae family, which is indigenous to China. It has valuable pharmacological properties, such as antimalarial, anti-inflammatory, and anticancer properties. However, whether it possesses antiasthma properties is unknown. In the current study, chloroform extract ofArtemisia annuaL. (CEAA) was prepared, and we found that CEAA completely eliminated acetylcholine (ACh) or high K+-elicited (80 mM) contractions of mouse tracheal rings (TRs). Patch-clamp technique and ion channel blockers were employed to explore the underlying mechanisms of the relaxant effect of CEAA. In whole-cell current recording, CEAA almost fully abolished voltage-dependent Ca2+channel (VDCC) currents and markedly enhanced large conductance Ca2+-activated K+(BK) channel currents on airway smooth muscle cells (ASMCs). In single channel current recording, CEAA increased the opening probability but had no effect on the single channel conductance of BK channels. However, under paxilline-preincubated (a selective BK channel blocker) conditions, CEAA only slightly increased BK channel currents. These results indicate that CEAA may contain active components with potent antiasthma activity. The abolished VDCCs by CEAA may mainly contribute to the underlying mechanism through which it acts as an effective antiasthmatic compound, but the enhanced BK currents might play a less important role in the antiasthmatic effects.

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Role of calcium channel blockade in relaxation of tracheal smooth muscle by extracellular Mg2+

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1996.271.2.l251 ◽

1996 ◽

Vol 271 (2) ◽

pp. L251-L257 ◽

Cited By ~ 5

Author(s):

L. A. Sonna ◽

C. A. Hirshman ◽

T. L. Croxton

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Tracheal Smooth Muscle ◽

Positive Shift ◽

Whole Cell Patch Clamp ◽

Current Voltage ◽

Voltage Dependent ◽

Steady State Inactivation ◽

Slope Factor ◽

Channel Currents

Magnesium ion (Mg2+) is a bronchodilator, but little is known about its mechanism of action on airways. We hypothesized that Mg2+ inhibits voltage-dependent Ca2+ channels of airway smooth muscle. Smooth muscle cells were freshly dispersed from pig trachea with collagenase. Depolarization-induced inward Ca2+ currents, measured in whole cell patch-clamp experiments, were inhibited by nifedipine and stimulated by BAY K 8644. Increasing bath Mg2+ from 1 to 21 mM caused a reversible approximately 30% inhibition of current and a positive shift of the peak current-voltage relationship. Voltage-dependent steady-state inactivation had a half-maximal potential (Vh) of -12 mV and a Boltzmann slope factor (k) of 6.0 mV. High Mg2+ caused a positive shift in Vh without affecting k, whereas nifedipine caused a negative shift in Vh and increased k. The inhibition of voltage-dependent Ca2+ channel currents by Mg2+ was quantitatively similar to Mg(2+)-induced relaxation of KCl-contracted tracheal smooth muscle strips. We conclude that inhibition of Ca2+ influx through dihydropyridine-sensitive, voltage-dependent channels by Mg2+ accounts for much of its relaxant action on airway smooth muscle.

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Inhibitory Effects of Diazepam and Midazolam on Ca2+and K+Channels in Canine Tracheal Smooth Muscle Cells

Anesthesiology ◽

10.1097/00000542-199901000-00026 ◽

1999 ◽

Vol 90 (1) ◽

pp. 197-207 ◽

Cited By ~ 22

Author(s):

Michiaki Yamakage ◽

Takashi Matsuzaki ◽

Naoki Tsujiguchi ◽

Yasuyuki Honma ◽

Akiyoshi Namiki

Keyword(s):

Smooth Muscle ◽

Smooth Muscle Cells ◽

Airway Smooth Muscle ◽

Muscle Relaxation ◽

Muscle Cells ◽

Tracheal Smooth Muscle ◽

Inhibitory Effects ◽

K Channels ◽

Voltage Dependent ◽

Channel Currents

Background Benzodiazepines have a direct bronchodilator action in airway smooth muscle, but the mechanisms by which these agents produce muscle relaxation are not fully understood. The current study was performed to identify the effects of the benzodiazepines diazepam and midazolam on Ca2+ and K+ channels in canine tracheal smooth muscle cells. Methods Whole-cell patch-clamp recording techniques were used to evaluate the effects of the benzodiazepines diazepam (10(-8) to 10(-3) M) and midazolam (10(-8) to 10(-3) M) on inward Ca2+ and outward K+ channel currents in dispersed canine tracheal smooth muscle cells. The effects of the antagonists flumazenil (10(-5) M) and PK11195 (10(-5) M) on these channels were also studied. Results Each benzodiazepine tested significantly inhibited Ca2+ currents in a dose-dependent manner, with 10(-6) M diazepam and 10(-5) M midazolam each causing approximately 50% depression of peak voltage-dependent Ca2+ currents. Both benzodiazepines promoted the inactivated state of the channel at more-negative potentials. The Ca2+-activated and voltage-dependent K+ currents were inhibited by diazepam and midazolam (> 10(-5) M and > 10(-4) M, respectively). Flumazenil and PK11195 had no effect on these channel currents or on the inhibitory effects of the benzodiazepines. Conclusions Diazepam and midazolam had inhibitory effects on voltage-dependent Ca2+ channels, which lead to muscle relaxation. However, high concentrations of these agents were necessary to inhibit the K+ channels. The lack of antagonized effects of their antagonists is related to the non-gamma-aminobutyric acid-mediated electrophysiologic effects of benzodiazepines on airway smooth muscle contractility.

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Intracellular pH regulates voltage-dependent Ca2+ channels in porcine tracheal smooth muscle cells

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1995.268.4.l642 ◽

1995 ◽

Vol 268 (4) ◽

pp. L642-L646 ◽

Cited By ~ 8

Author(s):

M. Yamakage ◽

K. S. Lindeman ◽

C. A. Hirshman ◽

T. L. Croxton

Keyword(s):

Smooth Muscle ◽

Smooth Muscle Cells ◽

Airway Smooth Muscle ◽

Muscle Cells ◽

Tracheal Smooth Muscle ◽

Airway Smooth Muscle Cells ◽

Smooth Muscle Contractility ◽

Voltage Dependent ◽

Airway Tone ◽

Ca2 Channels

Changes in CO2 or in pH modify airway smooth muscle contractility. To investigate the mechanisms involved, we compared K(+)-induced contractions in porcine bronchial rings exposed to different CO2 concentrations and directly measured the effects of changes in intracellular (pHi) or extracellular pH (pHo) on Ca2+ currents (ICa) through voltage-dependent Ca2+ channels (VDC) in porcine tracheal smooth muscle cells. Hypocapnia and hypercapnia caused leftward and rightward shifts, respectively, in the dose-response to K+ (P < 0.05) but did not change the maximum force obtained. Peak ICa (10 mM external Ca2+) elicited by depolarizing pulses from -80 mV was maximal [-265 +/- 12 pA (mean +/- SE), n = 19] at +10 mV. Intracellular acidification decreased the peak ICa at +10 mV from -261 +/- 20 pA to -177 +/- 12 pA (P < 0.05, n = 4), while intracellular alkalinization increased the peak ICa at +10 mV from -302 +/- 27 pA to -368 +/- 26 pA (P < 0.05, n = 4). Changes in pHo had little effect on ICa. There was no shift in the voltage-dependence of induced ICa with any change. We conclude that pHi, but not pHo, directly modulates the entry of Ca2+ into airway smooth muscle cells through VDC. This mechanism may contribute to regulation of airway tone by CO2.

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Two distinct effects of PIP2 underlie auxiliary subunit-dependent modulation of Slo1 BK channels

The Journal of General Physiology ◽

10.1085/jgp.201511363 ◽

2015 ◽

Vol 145 (4) ◽

pp. 331-343 ◽

Cited By ~ 9

Author(s):

Yutao Tian ◽

Florian Ullrich ◽

Rong Xu ◽

Stefan H. Heinemann ◽

Shangwei Hou ◽

...

Keyword(s):

Divalent Cation ◽

Critical Role ◽

Cell Types ◽

Bk Channels ◽

Bk Channel ◽

Positive Direction ◽

Human Embryonic Kidney Cells ◽

Auxiliary Subunits ◽

Voltage Dependent ◽

Negative Surface

Phosphatidylinositol 4,5-bisphosphate (PIP2) plays a critical role in modulating the function of numerous ion channels, including large-conductance Ca2+- and voltage-dependent K+ (BK, Slo1) channels. Slo1 BK channel complexes include four pore-forming Slo1 (α) subunits as well as various regulatory auxiliary subunits (β and γ) that are expressed in different tissues. We examined the molecular and biophysical mechanisms underlying the effects of brain-derived PIP2 on human Slo1 BK channel complexes with different subunit compositions that were heterologously expressed in human embryonic kidney cells. PIP2 inhibited macroscopic currents through Slo1 channels without auxiliary subunits and through Slo1 + γ1 complexes. In contrast, PIP2 markedly increased macroscopic currents through Slo1 + β1 and Slo1 + β4 channel complexes and failed to alter macroscopic currents through Slo1 + β2 and Slo1 + β2 Δ2–19 channel complexes. Results obtained at various membrane potentials and divalent cation concentrations suggest that PIP2 promotes opening of the ion conduction gate in all channel types, regardless of the specific subunit composition. However, in the absence of β subunits positioned near the voltage-sensor domains (VSDs), as in Slo1 and probably Slo1 + γ1, PIP2 augments the negative surface charge on the cytoplasmic side of the membrane, thereby shifting the voltage dependence of VSD-mediated activation in the positive direction. When β1 or β4 subunits occupy the space surrounding the VSDs, only the stimulatory effect of PIP2 is evident. The subunit compositions of native Slo1 BK channels differ in various cell types; thus, PIP2 may exert distinct tissue- and divalent cation–dependent modulatory influences.

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Inhibition of dihydropyridine-sensitive calcium entry in hypoxic relaxation of airway smooth muscle

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1995.268.2.l201 ◽

1995 ◽

Vol 268 (2) ◽

pp. L201-L206 ◽

Cited By ~ 2

Author(s):

C. Vannier ◽

T. L. Croxton ◽

L. S. Farley ◽

C. A. Hirshman

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Muscle Tone ◽

Bay K 8644 ◽

O2 Concentration ◽

Voltage Dependent ◽

Progressive Hypoxia ◽

Carbamyl Choline

Hypoxia dilates airways in vivo and reduces active tension of airway smooth muscle in vitro. To determine whether hypoxia impairs Ca2+ entry through voltage-dependent channels (VDC), we tested the ability of dihydropyridines to modulate hypoxia-induced relaxation of KCl- and carbamyl choline (carbachol)-contracted porcine bronchi. Carbachol- or KCl-contracted bronchial rings were exposed to progressive hypoxia in the presence or absence of 1 microM BAY K 8644 (an L-type-channel agonist). In separate experiments, rings were contracted with carbachol or KCl, treated with nifedipine (a VDC antagonist), and finally exposed to hypoxia. BAY K 8644 prevented hypoxia-induced relaxation in KCl-contracted bronchi. Nifedipine (10(-5) M) totally relaxed KCl- contracted bronchi. Carbachol-contracted bronchi were only partially relaxed by nifedipine but were completely relaxed when the O2 concentration of the gas was reduced from 95 to 0%. These data indicate that hypoxia can reduce airway smooth muscle tone by limiting entry of Ca2+ through a dihydropyridine-sensitive pathway, but that other mechanisms also contribute to hypoxia-induced relaxation of carbachol-contracted bronchi.

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Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

AJP Cell Physiology ◽

10.1152/ajpcell.00325.2013 ◽

2014 ◽

Vol 306 (5) ◽

pp. C460-C470 ◽

Cited By ~ 18

Author(s):

Kiril L. Hristov ◽

Amy C. Smith ◽

Shankar P. Parajuli ◽

John Malysz ◽

Georgi V. Petkov

Keyword(s):

Smooth Muscle ◽

Membrane Potential ◽

Guinea Pig ◽

Bk Channels ◽

Bk Channel ◽

K Channel ◽

Channel Activity ◽

Open Probability ◽

Channel Regulation ◽

Pkc Activation

Large-conductance voltage- and Ca2+-activated K+ (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca2+ imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca2+ levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca2+-dependent mechanism, thus increasing DSM contractility.

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