The restriction of diffusion of cations at the external surface of cardiac myocytes varies between species

Yao, Atsushi; Spitzer, Kenneth W.; Ito, Nobuhiko; Zaniboni, Massimiliano; Lorell, Beverly H.; Barry, William H.

doi:10.1016/s0143-4160(97)90070-1

Cited by 43 publications

(48 citation statements)

References 20 publications

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“…2 One consequence of this network of narrow tubules is that a rapid change in the composition of the solution around a ventricular myocyte results in a slower change in the composition of the fluid within the t-tubules because of the time required for diffusion into the t-tubular network. In guinea pig myocytes, a rapid change of [Ca 2ϩ ] o results in the diffusion of Ca 2ϩ into the t-tubules at 3 to 16 m/s, 16 so that the solution change within the t-tubules is delayed by up to 2.3 seconds, and washout of Ca 2ϩ from the t-tubules occurs with a time constant of up to 1.7 seconds for the deeper regions of the t-tubular system, 16 although these time courses may vary between species, 17 possibly reflecting species differences in t-tubule morphology.…”

Section: Occurrence and Morphology Of The T-tubulesmentioning

confidence: 99%

T-Tubule Function in Mammalian Cardiac Myocytes

Brette

Orchard

2003

Circulation Research

333

296

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Abstract-The transverse tubules (t-tubules) of mammalian cardiac ventricular myocytes are invaginations of the surface membrane. Recent studies have suggested that the structure and function of the t-tubules are more complex than previously believed; in particular, many of the proteins involved in cellular Ca 2ϩ cycling appear to be concentrated at the t-tubule. Thus, the t-tubules are an important determinant of cardiac cell function, especially as the main site of excitation-contraction coupling, ensuring spatially and temporally synchronous Ca 2ϩ release throughout the cell. Changes in t-tubule structure and protein expression occur during development and in heart failure, so that changes in the t-tubules may contribute to the functional changes observed in these conditions. The purpose of this review is to provide an overview of recent studies of t-tubule structure and function in cardiac myocytes. Key Words: cardiac muscle Ⅲ t-tubules Ⅲ excitation-contraction coupling Ⅲ heart failure T he transverse tubules (t-tubules) of mammalian cardiac ventricular myocytes are invaginations of the surface membrane that occur at the Z line and have both transverse and longitudinal elements. Many of the proteins involved in excitation-contraction coupling appear to be concentrated at the t-tubules. Therefore, it has been suggested that the t-tubules play a central role in cell activation. In the present review, we will consider the immunohistochemical and functional evidence for protein localization at the t-tubules, potential problems in the interpretation of such data, and the functional consequences of such localization. We will also consider the possible role of the t-tubules in the functional changes that occur during cardiac development, hypertrophy, and failure. Occurrence and Morphology of the T-TubulesT-tubules are present in the cardiac tissue of all species of mammals so far investigated (eg, mice, 1 rats, 2 guinea pigs, 3 rabbits, 4 dogs, 5 pigs, 1 and humans 6 ) but appear to be absent in avian, 7 reptile 8 and amphibian 8 cardiac tissue. Within mammalian cardiac tissue, t-tubules occur predominantly in ventricular myocytes, being either absent or far less developed in atrial, pacemaking, and conducting tissue, 9 although a recent report has suggested that Ϸ50% of atrial myocytes possess a sparse irregular tubular system. 10 The following discussion will concentrate on mammalian ventricular myocytes.The t-tubules are invaginations of the sarcolemma and glycocalyx, which appears to remain associated with the sarcolemma within the t-tubules. 11 Early studies of cardiac muscle showed that they occur at the Z line, at the end of each sarcomere 12 ; therefore, they occur at intervals of Ϸ2 m along the longitudinal axis of the ventricular myocyte. Subsequent studies have shown that the t-tubular system also has longitudinal extensions. 13 Although the t-tubules leave the surface membrane at the Z line, forming an approximately rectangular array, only Ϸ60% of the tubular volume occurs near the Z line; the other 40% ...

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Section: Occurrence and Morphology Of The T-tubulesmentioning

confidence: 99%

T-Tubule Function in Mammalian Cardiac Myocytes

Brette

Orchard

2003

Circulation Research

333

296

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“…We usually made our observations of myocyes at the center of the Z axis. The images were stored digitally (512 × 480 pixels/frame, 8-bit) ] i transients were evoked by exposing one end of a fluo-3 loaded atrial or ventricular myocyte to 10 mM caffeine for 500 ms with a rapid solution-switcher device, which changes the solution bathing a cell in 3-4 ms [19,20]. The activation of the rapid solution-switcher device was delivered 10 s after an electrically stimulated contraction.…”

Section: +mentioning

confidence: 99%

Difference in Propagation of Ca2+ Release in Atrial and Ventricular Myocytes

Tanaami

Ishida

Seguchi

et al. 2005

JJP

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within the myocytes. In contrast, mammalian atrial myocytes do not have a well developed t-tubular system, and the coupling between the L-type Ca 2+ channels in the sarcolemma and the junctional SR occurs around the periphery of the myocytes [6][7][8]. A confocal imaging of [Ca 2+ ] i has shown that in mammalian atrial myocytes during E-C coupling, an increase in [Ca 2+ ] i can be observed in the peripheral regions of the cell before it spreads to the center [9][10][11]. Furthermore, in spite of a poorly developed t-tubular system, ryanodine receptors (RyR) are present at seemingly equal abundance through atrial myocytes [11][12][13]. These observations strongly suggest that many RyR in the central SR are not associated with L-type Ca 2+ channels. It has been proposed

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“…To observe the effects of STX (B19491, Calbiochem, San Diego, CA; 39H1139, Sigma-Aldrich, St. Louis, MO) and TTX (99H0832; Sigma-Aldrich) on [Ca 2ϩ ] i transients, sodium currents and/or L-type calcium currents, we rapidly applied those drugs to clamped single cells. Rapid applications of STX and TTX were accomplished with a fast solution switcher device (Yao et al, 1997), which minimizes the amounts of test solution required and eliminates uncertainty regarding the precise time of exposure.…”

Section: Dissociation Of Adult Mouse Ventricular Myocytesmentioning

confidence: 99%

Saxitoxin Blocks L-TypeI_Ca

Sheets²,

Ishida

et al. 2003

J Pharmacol Exp Ther

Self Cite

124

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Saxitoxin (STX) and tetrodotoxin (TTX) are frequently used to selectively block sodium channels. In this study, we provide evidence that commercial STX also inhibits L-type Ca 2ϩ currents (I Ca,L ) in adult mouse ventricular myocytes (VMs) and tsA-201 cells that were transiently cotransfected with three calcium channel subunits. We measured inhibition of sodium currents (I Na ) in mouse VMs, of I Ca,L in mouse VM and tsA-201 cells, and intracellular calcium concentration ([Ca 2ϩ ] i ) transients in single mouse VMs. STX or TTX was abruptly applied before the test voltage pulse using a rapid solution switcher device. STX (10 M; Calbiochem) and TTX (60 M; Sigma-Aldrich) completely blocked I Na in mouse VMs. However, STX at 10 M also reduced I Ca,L in mouse VM by 39% (P Ͻ 0.0001; n ϭ 14), whereas TTX at 60 M had no effect on I Ca,L . STX (10 M; Calbiochem) reduced the amplitude of the [Ca 2ϩ ] i transients in mouse VMs by 36% (P Ͻ 0.0001; n ϭ 10). In contrast, TTX (60 M; Sigma-Aldrich) only reduced the amplitude of the [Ca 2ϩ ] i transients by 9% (P ϭ 0.003; n ϭ 5). STX (10 M) obtained from Sigma-Aldrich showed a similar inhibitory effect on I Ca,L (33%) (P Ͻ 0.0001; n ϭ 5) in mouse VMs. STX (Calbiochem) inhibited the calcium currents of tsA-201 cells in a dose-dependent manner. This inhibition was voltage-independent. The currentvoltage relationship of calcium currents in tsA-201 cells was not altered by STX. These results indicate that STX partially blocks L-type Ca 2ϩ channels and thus provide further evidence that its effects are not specific for Na ϩ channels.Saxitoxin (STX) and tetrodotoxin (TTX) have been well known sodium channel blockers. They are frequently used to selectively block sodium currents in studies of sodium channels and other membrane currents such as I Ca,L (Jones and Marks, 1989;Sheets et al., 1996;Vites and Wasserstrom, 1996;Penzotti et al., 1998;Su et al., 2001 Materials and Methods Dissociation of Adult Mouse Ventricular Myocytes.Single mouse ventricular myocytes were isolated as described previously (Yao et al., 1998). After retrograde perfusion with modified Tyrode's solution (Ca 2ϩ -free) for 5 min, the heart was digested for 7 to 12 min with 0.9 mg/ml collagenase D (Roche Diagnostics, Indianapolis, IN) in modified Tyrode's solution containing 25 M CaCl 2 . The modified Tyrode's solution (pH 7.4) contained the following: 126 mM NaCl, 4.4 mM KCl, 1.0 mM MgCl 2 , 18 mM NaHCO 3 , 11 mM glucose, 4 mM HEPES, 30 mM butanedione monoxime, and 0.13 U/ml insulin, and was gassed with 5% CO 2 , 95% O 2 . The digested left ventricle was cut into small pieces in modified Tyrode's solution containing 100 M Ca 2ϩ . These pieces were gently agitated to release single myocytes and then incubated in the same solution with 2% albumin at 30°C for 20 min. The cell suspension was centrifuged at 300 rpm for 3 min, and the pellet of cells was resuspended in modified Tyrode's solution containing 200 M Ca 2ϩ and 2% albumin and allowed to settle for another 20 min at 30°C. Cells were then suspende...

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The restriction of diffusion of cations at the external surface of cardiac myocytes varies between species

Cited by 43 publications

References 20 publications

T-Tubule Function in Mammalian Cardiac Myocytes

T-Tubule Function in Mammalian Cardiac Myocytes

Difference in Propagation of Ca2+ Release in Atrial and Ventricular Myocytes

Saxitoxin Blocks L-TypeI_Ca

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The restriction of diffusion of cations at the external surface of cardiac myocytes varies between species

Cited by 43 publications

References 20 publications

T-Tubule Function in Mammalian Cardiac Myocytes

T-Tubule Function in Mammalian Cardiac Myocytes

Difference in Propagation of Ca2+ Release in Atrial and Ventricular Myocytes

Saxitoxin Blocks L-TypeICa

Contact Info

Product

Resources

About

Saxitoxin Blocks L-TypeI_Ca