scholarly journals β-Adrenergic Regulation of Cyclic AMP and Ca Current at the T-Tubules and Surface Membrane in Rat Cardiomyocytes

2014 ◽  
Vol 106 (2) ◽  
pp. 304a
Author(s):  
Rodolphe Fischmeister ◽  
Cristina E. Molina ◽  
Youn Kyoung Son
Keyword(s):  
Cyclic Amp ◽  
Surface Membrane ◽  
Ca Current ◽  
Rat Cardiomyocytes ◽  
Adrenergic Regulation ◽  
T Tubules

scholarly journals Slow diffusion of K+ in the T tubules of rat cardiomyocytes

2006 ◽  
Vol 101 (4) ◽  
pp. 1170-1176 ◽  
Author(s):  
Fredrik Swift ◽  
Tævje A. Strømme ◽  
Bjørn Amundsen ◽  
Ole M. Sejersted ◽  
Ivar Sjaastad
Keyword(s):  
Diffusion Rate ◽  
Osmotic Shock ◽  
Surface Membrane ◽  
Current Control ◽  
Rat Cardiomyocytes ◽  
Steady State Current ◽  
Cardiomyocyte Contractility ◽  
T Tubules ◽  
The Difference ◽  
The Times

Cardiomyocyte contractility is regulated by the extracellular K+ concentration ([K+]o). Potassium dynamics in the T tubules during the excitation-contraction cycle depends on the diffusion rate of K+, but this rate is not known. Detubulation of rat cardiomyocytes was induced by osmotic shock using formamide, which separated the surface membrane from the T tubules. Changes in current and membrane potential in voltage-clamped (−80 mV) and current-clamped control and detubulated cardiomyocytes were compared during rapid switches between 5.4 and 8.1 mM [K+]o, and the results were simulated in a mathematical model. In the voltage-clamp experiments, the current changed significantly slower in control than in detubulated cardiomyocytes during the switch from 5.4 to 8.1 mM [K+]o, as indicated by the times to achieve 25, 50, 90, and 95% of the new steady-state current [control (ms) t25 = 98 ± 12, t50 = 206 ± 20, t90 = 570 ± 72, t95 = 666 ± 92; detubulated t25 = 61 ± 11, t50 = 142 ± 17, t90 = 352 ± 52, t95 = 420 ± 69]. These time points were not significantly different either during the 8.1 to 5.4 mM [K+]o switch or in current-clamped cardiomyocytes switching from 5.4 to 8.1 mM [K+]o. Mathematical simulation of the difference current between control and detubulated cardiomyocytes gave a t-tubular diffusion rate for K+ of ∼85 μm2/s. We conclude that the diffusion of K+ in the T tubules is so slow that they constitute a functional compartment. This might play a key role in local regulation of the action potential, and thus in the regulation of cardiomyocyte contractility.

scholarly journals Altered Na/Ca exchange distribution in ventricular myocytes from failing hearts

2016 ◽  
Vol 310 (2) ◽  
pp. H262-H268 ◽  
Author(s):  
Hanne C. Gadeberg ◽  
Simon M. Bryant ◽  
Andrew F. James ◽  
Clive H. Orchard
Keyword(s):  
Heart Failure ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Coronary Artery Ligation ◽  
Sham Operation ◽  
Ca Current ◽  
Artery Ligation ◽  
Whole Cell ◽  
Rat Hearts ◽  
T Tubules

In mammalian cardiac ventricular myocytes, Ca efflux via Na/Ca exchange (NCX) occurs predominantly at T tubules. Heart failure is associated with disrupted t-tubular structure, but its effect on t-tubular function is less clear. We therefore investigated t-tubular NCX activity in ventricular myocytes isolated from rat hearts ∼18 wk after coronary artery ligation (CAL) or corresponding sham operation (Sham). NCX current ( INCX) and l-type Ca current ( ICa) were recorded using the whole cell, voltage-clamp technique in intact and detubulated (DT) myocytes; intracellular free Ca concentration ([Ca]i) was monitored simultaneously using fluo-4. INCX was activated and measured during application of caffeine to release Ca from sarcoplasmic reticulum (SR). Whole cell INCX was not significantly different in Sham and CAL myocytes and occurred predominantly in the T tubules in Sham myocytes. CAL was associated with redistribution of INCX and ICa away from the T tubules to the cell surface and an increase in t-tubular INCX/ ICa density from 0.12 in Sham to 0.30 in CAL myocytes. The decrease in t-tubular INCX in CAL myocytes was accompanied by an increase in the fraction of Ca sequestered by SR. However, SR Ca content was not significantly different in Sham, Sham DT, and CAL myocytes but was significantly increased by DT of CAL myocytes. In Sham myocytes, there was hysteresis between INCX and [Ca]i, which was absent in DT Sham but present in CAL and DT CAL myocytes. These data suggest altered distribution of NCX in CAL myocytes.

scholarly journals Adenoprotection of the heart involves phospholipase C-induced activation and translocation of PKC-ε to RACK2 in adult rat and mouse

2009 ◽  
Vol 297 (2) ◽  
pp. H718-H725 ◽  
Author(s):  
Richard A. Fenton ◽  
Satoshi Komatsu ◽  
Mitsuo Ikebe ◽  
Lynne G. Shea ◽  
James G. Dobson
Keyword(s):  
Confocal Microscopy ◽  
Phospholipase C ◽  
Adrenergic Agonist ◽  
Rat Cardiomyocytes ◽  
Scanning Confocal Microscopy ◽  
Adult Rat ◽  
Sds Page ◽  
T Tubules ◽  
Isolated Rat ◽  
Stimulation Of

Adenosine protects the heart from adrenergic overstimulation. This adenoprotection includes the direct anti-adrenergic action via adenosine A1 receptors (A1R) on the adrenergic signaling pathway. An indirect A1R-induced attenuation of adrenergic responsiveness involves the translocation of PKC-ε to t-tubules and Z-line of cardiomyocytes. We investigated with sarcomere imaging, immunocytochemistry imaging, and coimmunoprecipitation (co-IP) whether A1R activation of PKC-ε induces the kinase translocation to receptor for activated C kinase 2 (RACK2) in isolated rat and mouse hearts and whether phospholipase C (PLC) is involved. Rat cardiomyocytes were treated with the A1R agonist chlorocyclopentyladenosine (CCPA) and exposed to primary PKC-ε and RACK2 antibodies with secondaries conjugated to Cy3 and Cy5 (indodicarbocyanine), respectively. Scanning confocal microscopy showed that CCPA caused PKC-ε to reversibly colocalize with RACK2 within 3 min. Additionally, rat and mouse hearts were perfused and stimulated with CCPA or phenylisopropyladenosine to activate A1R, or with phorbol 12-myristate 13-acetate to activate PKC. RACK2 was immunoprecipitated from heart extracts and resolved with SDS-PAGE. Western blotting showed that CCPA, phenylisopropyladenosine, and phorbol 12-myristate 13-acetate in the rat heart increased the PKC-ε co-IP with RACK2 by 186, 49, and >1,000%, respectively. The A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine prevented the CCPA-induced co-IP with RACK2. In mouse hearts, CCPA increased the co-IP of PKC-ε with RACK2 by 61%. With rat cardiomyocytes, the β-adrenergic agonist isoproterenol increased sarcomere shortening by 177%. CCPA reduced this response by 47%, an action inhibited by the PLC inhibitor U-73122 and 8-cyclopentyl-1,3-dipropylxanthine. In conclusion, A1R stimulation of the heart is associated with PLC-initiated PKC-ε translocation and association with RACK2.

Subcellular distribution of sodium pump isoform subunits in mammalian cardiac myocytes

1996 ◽  
Vol 270 (4) ◽  
pp. C1221-C1227 ◽  
Author(s):  
A. A. McDonough ◽  
Y. Zhang ◽  
V. Shin ◽  
J. S. Frank
Keyword(s):  
Guinea Pig ◽  
Driving Force ◽  
Human Heart ◽  
Sodium Pump ◽  
Immunogold Labeling ◽  
Guinea Pig Heart ◽  
Rat Cardiomyocytes ◽  
Adult Rat ◽  
Na Pump ◽  
T Tubules

The cardiac Na+ pump (Na+ -K+ -ATPase) provides the driving force for the Na+/Ca2+ exchanger, a determinant of intracellular Ca2+ stores. Three Na+ pump alpha-catalytic subunit isoforms are expressed in human heart, alpha1 and alpha2 are expressed in rat heart, and only alpha1 is expressed in guinea pig heart. The objective of this study was to determine whether there are isoform-specific patterns of expression in the transverse tubules (T tubules) vs. the peripheral sarcolemma. In adult rat cardiomyocytes, anti-alpha1-specific antibodies labeled the T tubules more intensely than the peripheral sarcolemma, in which labeling was patchy, the same pattern reported for distribution of the Na+/Ca2+ exchanger (J. S. Frank, G. Mottino, D. Reid, R. S. Molday, and K. D. Philipson, J. Cell Biol. 117: 337-345, 1992), whereas anti-alpha2- and anti-beta1-antibodies uniformly labeled T tubules and peripheral sarcolemma. In guinea pig cardiomyocytes, an anti-alpha-antibody against an extracellular epitope evenly labeled the peripheral sarcolemma and T tubules, and immunogold labeling demonstrated coincidence of alpha-subunits and intramembranous particles in sarcolemma. In summary, Na+ pumps are located in both peripheral sarcolemma and T tubules of cardiomyocytes expressing either multiple or single Na+ pump isoforms.

Modulation of the response of a photosensitive muscle by β-adrenergic regulation of cyclic AMP levels

Nature ◽  
1984 ◽  
Vol 307 (5951) ◽  
pp. 551-553 ◽  
Author(s):  
L. J. Rubin ◽  
J. F. Nolte
Keyword(s):  
Cyclic Amp ◽  
Adrenergic Regulation

Antagonism by phosphate buffer of the twitch loss in isolated muscle fibers produced by calcium-free solutions

1978 ◽  
Vol 56 (3) ◽  
pp. 523-526 ◽  
Author(s):  
G. B. Frank
Keyword(s):  
Calcium Ions ◽  
Phosphate Buffer ◽  
Mechanical Response ◽  
Surface Membrane ◽  
Skeletal Muscle Fiber ◽  
Phosphate Ions ◽  
Membrane Bound ◽  
T Tubules ◽  
Time Required ◽  
External Calcium

In 37 of 41 isolated frog skeletal muscle fiber preparations (one, two, or three fibers) the twitch was eliminated or reduced to < 10% of control by exposing the fibers to a 0-caicium, bicarbonate-buffered solution for 10 min or less. Replacing the bicarbonate by a phosphate buffer either prevented twitch inhibition or increased the 0-calcium exposure time required for its production. It is concluded that surface membrane-bound calcium ions (presumably in the t-tubules) are required to couple the action potential to the mechanical response and that phosphate ions inhibit the loss of the membrane-bound calcium ions into an external calcium-free solution.

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