Abstract
The initiation of contraction in mammalian myocardial cells begins with the entry of Ca2+ through sarcolemmal Ca2+ channels (DHP-receptors) and triggering of Ca2+ release from the sarcoplasmic reticulum (SR) via Ca2+ release channels (ryanodine receptors; Näbaueret al., 1989). At the level of optical resolution (0.2–0.5 µm) the functional unit may be perceived as one sarcomere (1.6 to 2.2 tim z-line to z-line) of a single myofibril (diameter = 1 µm). This ”sarcomeric unit“ receives its Ca2+ from a collar of SR which forms dyadic junction with transverse tubules (t-tubules—invaginations of the surface membrane). Below the level of optical resolution, electron microscopy shows that each dyadic junction (0.1 µm diameter, about 30 nm wide) contains a number of DHP receptors in the t-tubular membrane and a larger number of ryanodine receptors opposing them in the SR membrane (Jorgensenet al.,1993; Carlet al., 1995). While there appear to be no mechanical contact between the two types of receptors in cardiac muscle (Sunet al.,1995), it is clear that their communication via rapid local rises in [Ca2+ i (Sham, Cleemann and Morad, 1995; Adachi-Akahane, Cleemann and Morad, 1996) and activation of Ca2+-induced Ca2+ release mechanism (CIRC; Fabiato, 1983, 1985) is of fundamental importance for the control of the cardiac contraction. Yet the details of this control process remains elusive. What is missing, in part, seems to be a clearer understanding of the way the DHP and ryanodine receptors interact in their normal environment. For instance, it is not clear whether the basic Ca2+ signaling unit (Ca2+ µ-domain) is a) a single ryanodine receptor responding to influx of Ca2+ via a single DHP receptor, b) a cluster of ryanodine receptors controlled by one DHP receptor, c) an entire dyadic junction with several DHP and Ryanodine receptors, or even d) an aborted Ca2+ wave spreading over several sarcomeric units.
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsPreview
Unable to display preview. Download preview PDF.
References
Adachi-Akahane, S., Cleemann, L., & Morad, M. (1996). Cross-signaling between L-type Ca’+ channel and ryanodine receptors in rat ventricular myocytes.Journal of General Physiology (in press).
Blatter, L. A., & Wier,W.G. (1990). Intracellular diffusion, binding, and compartmentalization of fluorescent calcium indicators indo-I and fura-2.Biophysical Journal,58: 1491–1499.
Cannell, M.B., Cheng, H., & Lederer, W.L. (1995). The control of calcium release in heart muscle.Science,268: 1045–1049.
Carl, S.L., Felix, K., Caswell, A.H., Brandt, N.R., Ball, W.J. Jr., Vaghy, P.L., Meissner, G., & Ferguson, D.G. (1995). Immunolocalization of sarcolemmal dihydropyridine receptor and sarcoplasmic reticulum triadin and ryanodine receptor in rabbit ventricular and atrial cells.Journal of Cell Biology,129: 673–682.
Cheng, H., Lederer, W.J., & Cannell, M.B. (1993). Calcium sparks: elementary events underlying excitation-contraction coupling in heart muscle.Science,262: 740–744.
Cleemann, L., & Morad, M. (1991). Role of Ca’’ channel in cardiac excitation-contraction coupling in the rat: Evidence from Ca“ transients and contraction.Journal of Physiology.432: 283–312.
Fabiato, A. (1983). Calcium-induced release of calcium from the cardiac sarcoplasmic reticulum.American Journal of Physiology,245:C 1-C 14.
Fabiato, A. (1985). Time and calcium dependence of activation and inactivation of calcium-induced release of calcium from sarcoplasmic reticulum of a skinned cardiac Purkinje cell.Journal of General Physiology,85: 247–289.
Hamill, O.P., Marty, A., Neher, E., Sakmann, B., & Sigworth, F.J. (1981). Improved patch-clamp technique for high resolution current recording from cells and cell-free membrane patches.Pflügers Archiv,191: 85–100.
Jorgensen, A.O., Shen, A.C.Y., Wayne, A., McPherson, P.S., & Campbell, K.P. (1993). The Ca“-release channel/ryanodine receptor is located in junctional and corbular sarcoplasmic reticulum in cardiac muscle.Journal of Cell Biology,120: 969–980.
Lipp, P., & Niggli, E. (1993). Microscopic spiral waves reveal positive feedback in subcellular calcium signaling.Biophysical Journal,65: 2272–2276.
Lopez-Lopez, J.R., Shacklock, P.S., Balke, C.W., & Wier, W.G. (1994). Local, stochastic release of Ca’* in volt- age-clamped rat heart cells: visualization with confocal microscopy.Journal of Physiology,480: 21–29.
Näbauer, M., Callewaert, G., Cleemann, L., & Morad, M. (1989). Regulation of calcium release is gated by calcium current, not gating charge in cardiac myocytes.Science,244: 800–803.
Niggli, E., & Lipp, P. (1992). Spatially restricted Ca“-release in cardiac myocytes revealed by confocal microscopy.Pflügers Archly, 420:suppl. I, R81.
O’Malley, D.M. (1994). Calcium permeability of the neuronal nuclear envelope: Evaluation using confocal volumes and intracellular perfusion.Journal of Neuroscience,14: 5741–5758.
Santana, L.F., Cheng, H., Gomez, A.M., Cannell, M.B., & Lederer, W.J. (1996). Relation between the sarcolemmal Ca“ current and Ca” sparks and local control theories for cardiac excitation-contraction coupling.Circulation Research,78: 166–171.
Sham, J. S. K., Cleemann, L., & Morad, M. (1995). Functional coupling of Ca“ channels and ryanodine receptors in cardiac muscle.PNAS,92: 121–125.
Shacklock, P.S., Wier, W.G., & Balke, C.W. (1995). Local Ca’’ transient (Ca’’ sparks) originate at transverse tubules in rat heart cells.Journal of Physiology,487: 601–608.
Smith, G.D., Wagner, J., & Keizer, J. (1996). Validity of rapid buffering approximation near a point source of calcium ions.Biophysical Journal,70: 2527–2539.
Stern, M.D. (1992). Buffering of calcium in the vicinity of a channel pore.Cell Calcium,13: 183–192.
Sun, X.H., Protasi, P., Takahashi, M., Takeshima, H., Ferguson, D.G., & Franzini-Armstrong, C. (1995). Molecu-lar architecture of membranes involved in excitation-contraction coupling of cardiac muscle.Journal ofCell Biology,129: 659–671.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 1997 Springer Science+Business Media New York
About this chapter
Cite this chapter
Cleeman, L., Wang, W., Morad, M. (1997). Rapid Confocal Measurements of Ca2+ Sparks in Rat Ventricular Myocytes. In: Sotelo, J.R., Benech, J.C. (eds) Calcium and Cellular Metabolism. Springer, Boston, MA. https://doi.org/10.1007/978-1-4757-9555-4_3
Download citation
DOI: https://doi.org/10.1007/978-1-4757-9555-4_3
Publisher Name: Springer, Boston, MA
Print ISBN: 978-1-4757-9557-8
Online ISBN: 978-1-4757-9555-4
eBook Packages: Springer Book Archive