Biophys J, November 2001, p. 2590-2605, Vol. 81, No. 5

Activation and Propagation of Ca²⁺ Release during Excitation-Contraction Coupling in Atrial Myocytes

Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois 60153, USA

Fast two-dimensional confocal microscopy and the Ca²⁺ indicator fluo-4 were used to study excitation-contraction (E-C) coupling in cat atrial myocytes which lack transverse tubules and contain both subsarcolemmal junctional (j-SR) and central nonjunctional (nj-SR) sarcoplasmic reticulum. Action potentials elicited by field stimulation induced transient increases of intracellular Ca²⁺ concentration ([Ca²⁺]_i) that were highly inhomogeneous. Increases started at distinct subsarcolemmal release sites spaced ~2 µm apart. The amplitude and the latency of Ca²⁺ release from these sites varied from beat to beat. Subsarcolemmal release fused to build a peripheral ring of elevated [Ca²⁺]_i, which actively propagated to the center of the cells via Ca²⁺-induced Ca²⁺ release. Resting myocytes exhibited spontaneous Ca²⁺ release events, including Ca²⁺ sparks and local (microscopic) or global (macroscopic) [Ca²⁺]_i waves. The microscopic [Ca²⁺]_i waves propagated in a saltatory fashion along the sarcolemma ("coupled" Ca²⁺ sparks) revealing the sequential activation of Ca²⁺ release sites of the j-SR. Moreover, during global [Ca²⁺]_i waves, Ca²⁺ release was evident from individual nj-SR sites. Ca²⁺ release sites were arranged in a regular three-dimensional grid as deduced from the functional data and shown by immunostaining of ryanodine receptor Ca²⁺ release channels. The longitudinal and transverse distances between individual Ca²⁺ release sites were both ~2 µm. Furthermore, electron microscopy revealed a continuous sarcotubular network and one peripheral coupling of j-SR with the sarcolemma per sarcomere. The results demonstrate directly that, in cat atrial myocytes, the action potential-induced whole-cell [Ca²⁺]_i transient is the spatio-temporal summation of Ca²⁺ release from subsarcolemmal and central sites. First, j-SR sites are activated in a stochastic fashion by the opening of voltage-dependent sarcolemmal Ca²⁺ channels. Subsequently, nj-SR sites are activated by Ca²⁺-induced Ca²⁺ release propagating from the periphery.

Biophys J, November 2001, p. 2590-2605, Vol. 81, No. 5
© 2001 by the Biophysical Society   0006-3495/01/11/2590/16  $2.00

This article has been cited by other articles:

				J. Kockskamper, L. Seidlmayer, S. Walther, K. Hellenkamp, L. S. Maier, and B. Pieske Endothelin-1 enhances nuclear Ca2+ transients in atrial myocytes through Ins(1,4,5)P3-dependent Ca2+ release from perinuclear Ca2+ stores J. Cell Sci., January 15, 2008; 121(2): 186 - 195. [Abstract] [Full Text] [PDF]

				L. T. Izu, T. Banyasz, C. W. Balke, and Y. Chen-Izu Eavesdropping on the Social Lives of Ca2+ Sparks Biophys. J., November 15, 2007; 93(10): 3408 - 3420. [Abstract] [Full Text] [PDF]

				P. Dan, E. Lin, J. Huang, P. Biln, and G. F. Tibbits Three-Dimensional Distribution of Cardiac Na+-Ca2+ Exchanger and Ryanodine Receptor during Development Biophys. J., October 1, 2007; 93(7): 2504 - 2518. [Abstract] [Full Text] [PDF]

				H. E. D. J. ter Keurs and P. A. Boyden Calcium and Arrhythmogenesis Physiol Rev, April 1, 2007; 87(2): 457 - 506. [Abstract] [Full Text] [PDF]

				M. D. Bootman, D. R. Higazi, S. Coombes, and H. L. Roderick Calcium signalling during excitation-contraction coupling in mammalian atrial myocytes. J. Cell Sci., October 1, 2006; 119(Pt 19): 3915 - 3925. [Abstract] [Full Text] [PDF]

				Y. Chen-Izu, S. L. McCulle, C. W. Ward, C. Soeller, B. M. Allen, C. Rabang, M. B. Cannell, C. W. Balke, and L. T. Izu Three-Dimensional Distribution of Ryanodine Receptor Clusters in Cardiac Myocytes Biophys. J., July 1, 2006; 91(1): 1 - 13. [Abstract] [Full Text] [PDF]

				L. T. Izu, S. A. Means, J. N. Shadid, Y. Chen-Izu, and C. W. Balke Interplay of Ryanodine Receptor Distribution and Calcium Dynamics Biophys. J., July 1, 2006; 91(1): 95 - 112. [Abstract] [Full Text] [PDF]

				K. A. Sheehan, A. V. Zima, and L. A. Blatter Regional differences in spontaneous Ca2+ spark activity and regulation in cat atrial myocytes J. Physiol., May 1, 2006; 572(3): 799 - 809. [Abstract] [Full Text] [PDF]

				L.-Z. Yang, J. Kockskamper, F. R. Heinzel, M. Hauber, S. Walther, J. Spiess, and B. Pieske Urocortin II enhances contractility in rabbit ventricular myocytes via CRF2 receptor-mediated stimulation of protein kinase A Cardiovasc Res, February 1, 2006; 69(2): 402 - 411. [Abstract] [Full Text] [PDF]

				S.-H. Woo, L. Cleemann, and M. Morad Diversity of atrial local Ca2+ signalling: evidence from 2-D confocal imaging in Ca2+-buffered rat atrial myocytes J. Physiol., September 15, 2005; 567(3): 905 - 921. [Abstract] [Full Text] [PDF]

				J. Kockskamper, A. V. Zima, and L. A. Blatter Modulation of sarcoplasmic reticulum Ca2+ release by glycolysis in cat atrial myocytes J. Physiol., May 1, 2005; 564(3): 697 - 714. [Abstract] [Full Text] [PDF]

				C. G. Perez, J. A. Copello, Y. Li, K. L. Karko, L. Gomez, J. Ramos-Franco, M. Fill, A. L. Escobar, and R. Mejia-Alvarez Ryanodine receptor function in newborn rat heart Am J Physiol Heart Circ Physiol, May 1, 2005; 288(5): H2527 - H2540. [Abstract] [Full Text] [PDF]

				M. H. P. Wussling, I. Aurich, O. Knauf, H. Podhaisky, and H.-J. Holzhausen Disposition of Calcium Release Units in Agarose Gel for an Optimal Propagation of Ca2+ Signals Biophys. J., December 1, 2004; 87(6): 4333 - 4342. [Abstract] [Full Text] [PDF]

				E. D. Moore, T. Voigt, Y. M. Kobayashi, G. Isenberg, F. S. Fay, M. F. Gallitelli, and C. Franzini-Armstrong Organization of Ca2+ Release Units in Excitable Smooth Muscle of the Guinea-Pig Urinary Bladder Biophys. J., September 1, 2004; 87(3): 1836 - 1847. [Abstract] [Full Text] [PDF]

				J. Kockskamper, G. U. Ahmmed, A. V. Zima, K. A. Sheehan, H. G. Glitsch, and L. A. Blatter Palytoxin disrupts cardiac excitation-contraction coupling through interactions with P-type ion pumps Am J Physiol Cell Physiol, August 1, 2004; 287(2): C527 - C538. [Abstract] [Full Text] [PDF]

				S.-Q. Wang, C. Wei, G. Zhao, D. X.P. Brochet, J. Shen, L.-S. Song, W. Wang, D. Yang, and H. Cheng Imaging Microdomain Ca2+ in Muscle Cells Circ. Res., April 30, 2004; 94(8): 1011 - 1022. [Abstract] [Full Text] [PDF]

				A. V. Zima and L. A. Blatter Inositol-1,4,5-trisphosphate-dependent Ca2+ signalling in cat atrial excitation-contraction coupling and arrhythmias J. Physiol., March 15, 2004; 555(3): 607 - 615. [Abstract] [Full Text] [PDF]

				S. P. Parsons and T. B. Bolton Localised calcium release events in cells from the muscle of guinea-pig gastric fundus J. Physiol., February 1, 2004; 554(3): 687 - 705. [Abstract] [Full Text] [PDF]

				S.-H. Woo, L. Cleemann, and M. Morad Spatiotemporal Characteristics of Junctional and Nonjunctional Focal Ca2+ Release in Rat Atrial Myocytes Circ. Res., January 10, 2003; 92 (1): e1 - e11. [Abstract] [Full Text] [PDF]

				A. Michailova, F. DelPrincipe, M. Egger, and E. Niggli Spatiotemporal Features of Ca2+ Buffering and Diffusion in Atrial Cardiac Myocytes with Inhibited Sarcoplasmic Reticulum Biophys. J., December 1, 2002; 83(6): 3134 - 3151. [Abstract] [Full Text] [PDF]

				F. Brette, K. Komukai, and C. H. Orchard Validation of formamide as a detubulation agent in isolated rat cardiac cells Am J Physiol Heart Circ Physiol, October 1, 2002; 283(4): H1720 - H1728. [Abstract] [Full Text] [PDF]

				Z. Yang, C. Pascarel, D.S. Steele, K. Komukai, F. Brette, and C.H. Orchard Na+-Ca2+ Exchange Activity Is Localized in the T-Tubules of Rat Ventricular Myocytes Circ. Res., August 23, 2002; 91(4): 315 - 322. [Abstract] [Full Text] [PDF]