Heteromeric Channels Formed From Alternating Kv7.4 and Kv7.5 α-Subunits Display Biophysical, Regulatory, and Pharmacological Characteristics of Smooth Muscle M-Currents

Electrical excitability, which plays an important role in excitation-contraction coupling in the pulmonary vasculature, is regulated by transmembrane ion flux in pulmonary artery smooth muscle cells (PASMC). This study examined the heterogeneous nature of native voltage-dependent K+ channels in human PASMC. Both voltage-gated K+ (KV) currents and Ca2+-activated K+ (KCa) currents were observed and characterized. In cell-attached patches of PASMC bathed in Ca2+-containing solutions, depolarization elicited a wide range of K+ unitary conductances (6–290 pS). When cells were dialyzed with Ca2+-free and K+-containing solutions, depolarization elicited four components of KV currents in PASMC based on the kinetics of current activation and inactivation. Using RT-PCR, we detected transcripts of 1) 22 KV channel α-subunits (KV1.1–1.7, KV1.10, KV2.1, KV3.1, KV3.3–3.4, KV4.1–4.2, KV5.1, KV 6.1–6.3, KV9.1, KV9.3, KV10.1, and KV11.1), 2) three KV channel β-subunits (KVβ1–3), 3) four KCa channel α-subunits ( Slo-α1 and SK2–SK4), and 4) four KCa channel β-subunits (KCaβ1–4). Our results show that human PASMC exhibit a variety of voltage-dependent K+ currents with variable kinetics and conductances, which may result from various unique combinations of α- and β-subunits forming the native channels. Functional expression of these channels plays a critical role in the regulation of membrane potential, cytoplasmic Ca2+, and pulmonary vasomotor tone.

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An Arg-Gly-Asp peptide stimulates constriction in rat afferent arteriole

AJP Renal Physiology ◽

10.1152/ajprenal.1997.273.5.f768 ◽

1997 ◽

Vol 273 (5) ◽

pp. F768-F776 ◽

Cited By ~ 13

Author(s):

Kay-Pong Yip ◽

Donald J. Marsh

Keyword(s):

Smooth Muscle ◽

Rat Kidney ◽

No Production ◽

Afferent Arteriole ◽

Calcium Dependent ◽

Endogenous Nitric Oxide ◽

Arginine Glycine Aspartic Acid ◽

Dose Dependent ◽

Α Subunits

The potential role of integrins in the myogenic mechanism was studied in the rat afferent arteriole (AA) by fluorescence immunolocalization and microperfusion of isolated AA. Confocal fluorescence images were acquired from frozen sections of rat kidney after indirect immunostaining for various integrin β- and α-subunits. The β1-, β3-, α3-, α5-, and αV-integrins were found on the plasma membrane in smooth muscle of AA, providing the morphological basis for participation of integrins in mechanotransduction. With 1 mM nitro-l-arginine methyl ester (l-NAME) in the luminal perfusate to inhibit endogenous nitric oxide (NO) production from AA, the hexapeptide GRGDSP (10−7–10−3 M) induced immediate vasoconstriction. The constriction was dose dependent and specific for peptides with arginine-glycine-aspartic acid (RGD) motifs, commonly found on the binding sites of extracellular matrix to integrins. In controls, the hexapeptide GRGESP induced no constriction. GRGDSP, 1 mM, induced a 21.6 ± 2.6% decrease ( P < 0.05, n = 6) in lumen diameter for 30 s and an 18.3 ± 4.1% increase ( P < 0.05, n = 6) in smooth muscle intracellular calcium concentration for 18 s, as measured by the emission ratio of Fluo-3/Fura Red. Binding of exogenous RGD motifs with exposed integrins on AA smooth muscle therefore triggers calcium-dependent vasoconstriction. However, the dose response to RGD was not sensitive to the myogenic tone of the vessel, which suggests that the integrin-mediated vasoconstriction is different from myogenic constriction.

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Mutation of protein kinase C phosphorylation site S1076 on α-subunits affects BKCa channel activity in HEK-293 cells

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.90518.2008 ◽

2009 ◽

Vol 297 (4) ◽

pp. L758-L766 ◽

Cited By ~ 10

Author(s):

Shu Zhu ◽

Darren D. Browning ◽

Richard E. White ◽

David Fulton ◽

Scott A. Barman

Keyword(s):

Smooth Muscle ◽

Protein Kinase ◽

Phosphorylation Site ◽

Channel Activity ◽

Excitatory Effect ◽

Hek 293 ◽

Hek 293 Cells ◽

293 Cells ◽

Smooth Muscle Function ◽

Α Subunits

Large conductance, calcium- and voltage-activated potassium (BKCa) channels are important modulators of pulmonary vascular smooth muscle membrane potential, and phosphorylation of BKCa channels by protein kinases regulates pulmonary arterial smooth muscle function. However, little is known about the effect of phosphorylating specific channel subunits on BKCa channel activity. The present study was done to determine the effect of mutating protein kinase C (PKC) phosphorylation site serine 1076 (S1076) on transfected human BKCa channel α-subunits in human embryonic kidney (HEK-293) cells, a heterologous expression system devoid of endogenous BKCa channels. Results showed that mutating S1076 altered the effect of PKC activation on BKCa channels in HEK-293 cells. Specifically, the phospho-deficient mutation BKCa-α(S1076A)/β1 attenuated the excitatory effect of the PKC activator phorbol myristate acetate (PMA) on BKCa channels, whereas the phospho-mimetic mutation BKCa-α(S1076E)/β1 increased the excitatory effect of PMA on BKCa channels. In addition, the phospho-null mutation S1076A blocked the activating effect of cGMP-dependent protein kinase G (PKG) on BKCa channels. Collectively, these results suggest that specific putative PKC phosphorylation site(s) on human BKCa channel α-subunits influences BKCa channel activity, which may subsequently alter pulmonary vascular smooth muscle function and tone.

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The extracellular loop of the auxiliary β1-subunit is involved in the regulation of BKCa channel mechanosensitivity

AJP Cell Physiology ◽

10.1152/ajpcell.00037.2018 ◽

2018 ◽

Vol 315 (4) ◽

pp. C485-C493 ◽

Cited By ~ 1

Author(s):

Fang Xin ◽

Yuan Cheng ◽

Jie Ren ◽

Sitao Zhang ◽

Ping Liu ◽

...

Keyword(s):

Smooth Muscle ◽

Patch Clamp ◽

Smooth Muscle Cells ◽

Single Channel ◽

Muscle Cells ◽

Hek293 Cells ◽

Bkca Channel ◽

Extracellular Loop ◽

Α Subunits ◽

Stretch Sensitivity

The large conductance Ca2+-activated potassium (BKCa) channel is activated by stretch. The stress-regulated exon (STREX) in α-subunits is known to affect the mechanosensitivity of BKCa channels. However, in human colonic smooth muscle cells (HCoSMCs), we found that the α-subunits without STREX (ZERO-BK) and β1-subunits could be detected yet the cells were mechanosensitive. Whether the β1-subunit is involved in the regulation of BKCa mechanosensitivity is unclear. In the present study, ZERO-BK and β1-subunits were individually expressed or coexpressed in HEK293 cells and cell-attached patch-clamp techniques were used to measure BKCa currents defining mechanosensitivity. Single-channel patch-clamp recordings from HEK293 cells cotransfected with ZERO-BK and β1-subunits showed stretch sensitivity, but there was no mechanosensitivity in HEK293 cells transfected only with ZERO-BK. We also showed that expression of the β1-subunit could increase mechanosensitivity of the STREX-type α-subunits (STREX-BK). To identify the domain in β1-subunits responsible for affecting stretch sensitivity, we expressed β1- LoopDel (chimeric β1-subunits without the extracellular loop) or β1- C TermDel (chimeric β1-subunits without COOH terminus) with ZERO-BK in HEK293 cells. The data showed that deletion of the extracellular loop but not the COOH terminus of β1-subunits virtually abolished the mechanosensitivity. These results suggest that the extracellular loop of the β1-subunit is involved in the regulation of BKCa channel mechanosensitivity and that role is independent of STREX.

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Inwardly rectifying potassium channels (KIR) in GtoPdb v.2021.3

IUPHAR/BPS Guide to Pharmacology CITE ◽

10.2218/gtopdb/f74/2021.3 ◽

2021 ◽

Vol 2021 (3) ◽

Author(s):

John P. Adelman ◽

David E. Clapham ◽

Hiroshi Hibino ◽

Atsushi Inanobe ◽

Lily Y. Jan ◽

...

Keyword(s):

Potassium Channels ◽

G Protein ◽

Inward Rectifier ◽

K Channel ◽

Domain Family ◽

K Channels ◽

Inwardly Rectifying Potassium Channels ◽

Inwardly Rectifying ◽

Α Subunits ◽

Heteromeric Channels

The 2TM domain family of K channels are also known as the inward-rectifier K channel family. This family includes the strong inward-rectifier K channels (Kir2.x) that are constitutively active, the G-protein-activated inward-rectifier K channels (Kir3.x) and the ATP-sensitive K channels (Kir6.x, which combine with sulphonylurea receptors (SUR1-3)). The pore-forming α subunits form tetramers, and heteromeric channels may be formed within subfamilies (e.g. Kir3.2 with Kir3.3).

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Inwardly rectifying potassium channels (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

IUPHAR/BPS Guide to Pharmacology CITE ◽

10.2218/gtopdb/f74/2019.4 ◽

2019 ◽

Vol 2019 (4) ◽

Author(s):

John P. Adelman ◽

David E. Clapham ◽

Hiroshi Hibino ◽

Atsushi Inanobe ◽

Lily Y. Jan ◽

...

Keyword(s):

Potassium Channels ◽

G Protein ◽

Inward Rectifier ◽

K Channel ◽

Domain Family ◽

K Channels ◽

Inwardly Rectifying Potassium Channels ◽

Inwardly Rectifying ◽

Α Subunits ◽

Heteromeric Channels

The 2TM domain family of K channels are also known as the inward-rectifier K channel family. This family includes the strong inward-rectifier K channels (Kir2.x) that are constitutively active, the G-protein-activated inward-rectifier K channels (Kir3.x) and the ATP-sensitive K channels (Kir6.x, which combine with sulphonylurea receptors (SUR1-3)). The pore-forming α subunits form tetramers, and heteromeric channels may be formed within subfamilies (e.g. Kir3.2 with Kir3.3).

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Deglycosylation of the β1-subunit of the BK channel changes its biophysical properties

AJP Cell Physiology ◽

10.1152/ajpcell.00116.2006 ◽

2006 ◽

Vol 291 (4) ◽

pp. C750-C756 ◽

Cited By ~ 13

Author(s):

Brian M. Hagen ◽

Kenton M. Sanders

Keyword(s):

Smooth Muscle ◽

Molecular Mass ◽

Single Channel ◽

Bk Channels ◽

Bk Channel ◽

Dependent Manner ◽

Biophysical Properties ◽

Single Channel Recordings ◽

Inside Out ◽

Α Subunits

Large-conductance Ca2+-activated potassium (BK) channels are composed of pore-forming α-subunits and auxiliary β-subunits. The α-subunits are widely expressed in many cell types, whereas the β-subunits are more tissue specific and influence diverse aspects of channel function. In the current study, we identified the presence of the smooth muscle-specific β1-subunit in murine colonic tissue using Western blotting. The native β1-subunits migrated in SDS-PAGE as two molecular mass bands. Enzymatic removal of N-linked glycosylations from the β1-subunit resulted in a single band that migrated at a lower molecular mass than the native β1-subunit bands, suggesting that the native β1-subunit exists in either a core glycosylated or highly glycosylated form. We investigated the functional consequence of deglycosylating the β1-subunit during inside-out single-channel recordings. During inside-out single-channel recordings, with N-glycosidase F in the pipette solution, the open probability ( Po) and mean open time of BK channels increased in a time-dependent manner. Deglycosylation of BK channels did not affect the conductance but shifted the steady-state voltage of activation toward more positive potentials without affecting slope when Ca2+ concentration was <1 μM. Treatment of myocytes lacking the β1-subunits of the BK channel with N-glycosidase F had no effect. These data suggest that glycosylations on the β1-subunit in smooth muscle cells can modify the biophysical properties of BK channels.

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The Cellular Origin in Atheromatous Lesion

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010006800x ◽

1970 ◽

Vol 28 ◽

pp. 202-203

Author(s):

T. M. Murad ◽

H. A. I. Newman ◽

K. F. Kern

Keyword(s):

Smooth Muscle ◽

Smooth Muscle Cells ◽

Rabbit Aorta ◽

Mixed Population ◽

The Other ◽

Cellular Origin ◽

Ultrastructural Studies ◽

Atherosclerotic Lesions ◽

Show Evidence ◽

Early Lesion

The origin of lipid containing cells in atheromatous lesion has been disputed. Geer in his study on atheromatous lesions of rabbit aorta, suggested that the early lesion is composed mainly of lipid-laden macrophages and the later lesion has a mixed population of macrophages and smooth muscle cells. Parker on the other hand, was able to show evidence that the rabbit lesion is primarily composed of lipid-laden cells of smooth muscle origin. The above studies and many others were done on an intact lesion without any attempt of cellular isolation previous to their ultrastructural studies. Cell isolation procedures have been established for atherosclerotic lesions through collagenase and elastase digestion Therefore this procedure can be utilized to identify the cells involved in rabbit atheroma.

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Electron Probe Analysis of Muscle

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100054583 ◽

1982 ◽

Vol 40 ◽

pp. 398-401

Author(s):

A. V. Somlyo ◽

H. Shuman ◽

A. P. Somlyo

Keyword(s):

Skeletal Muscle ◽

Smooth Muscle ◽

Sarcoplasmic Reticulum ◽

Resting State ◽

Binding Sites ◽

Electron Probe ◽

Frog Skeletal Muscle ◽

Electron Probe Analysis ◽

Probe Analysis

Electron probe analysis of frozen dried cryosections of frog skeletal muscle, rabbit vascular smooth muscle and of isolated, hyperpermeab1 e rabbit cardiac myocytes has been used to determine the composition of the cytoplasm and organelles in the resting state as well as during contraction. The concentration of elements within the organelles reflects the permeabilities of the organelle membranes to the cytoplasmic ions as well as binding sites. The measurements of [Ca] in the sarcoplasmic reticulum (SR) and mitochondria at rest and during contraction, have direct bearing on their role as release and/or storage sites for Ca in situ.

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