AJP - Cell Physiology, Vol 258, Issue 1 C189-C193, Copyright © 1990 by American Physiological Society

ARTICLES

Ca2(+)-induced Ca2+ release as examined by photolysis of caged Ca2+ in single ventricular myocytes

M. Nabauer and M. Morad
Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6085.

In cardiac muscle, entry of Ca2+ through the voltage-gated Ca2+ channel and its interaction with an intracellular site are thought to trigger the release of the intracellular Ca2+ pools and to activate contraction. The availability of a novel "caged calcium" compound, and its effective use in neuronal and heart cells to modulate Ca2+ channel and contraction, made it possible to examine directly the Ca2(+)-induced Ca2+ release hypothesis in intact mammalian cardiac myocytes. We used the caged Ca2+ compound DM-nitrophen, which on photolysis, rapidly (less than 200 microseconds) changes its Ca2(+)-binding affinity from 3 X 10(-9) to 2 X 10(-3) M at pH 7.0. In isolated whole cell clamped guinea pig ventricular myocytes dialyzed with unphotolyzed DM-nitrophen (Ca2+ buffered to values less than 10(-7) M), we found that a 160-microseconds light pulse photoreleased sufficient Ca2+ to activate contraction. Photorelease of Ca2+ failed to activate significant contraction in myocytes pretreated with caffeine, supporting the idea that the release of Ca2+ from intracellular pools was necessary to generate tension. However, photorelease of Ca2+ after the depolarization-induced Ca2+ release failed to suppress contraction, as predicted from the Ca2(+)-induced inactivation hypothesis. The failure to suppress contraction was not sufficient to definitively reject the Ca2(+)-induced inactivation hypothesis, since the intracellular Ca2+ concentration may not have risen sufficiently to inactivate the release channel.

This article has been cited by other articles:

				E. Savio-Galimberti and J. E. Ponce-Hornos Effects of caffeine, verapamil, lithium, and KB-R7943 on mechanics and energetics of rat myocardial bigeminies Am J Physiol Heart Circ Physiol, February 1, 2006; 290(2): H613 - H623. [Abstract] [Full Text] [PDF]

				R. Hinch A Mathematical Analysis of the Generation and Termination of Calcium Sparks Biophys. J., March 1, 2004; 86(3): 1293 - 1307. [Abstract] [Full Text] [PDF]

				E. A. Sobie, K. W. Dilly, J. dos Santos Cruz, W. J. Lederer, and M. S. Jafri Termination of Cardiac Ca2+ Sparks: An Investigative Mathematical Model of Calcium-Induced Calcium Release Biophys. J., July 1, 2002; 83(1): 59 - 78. [Abstract] [Full Text] [PDF]

				J. S. K. Sham, L.-S. Song, Y. Chen, L.-H. Deng, M. D. Stern, E. G. Lakatta, and H. Cheng Termination of Ca2+ release by a local inactivation of ryanodine receptors in cardiac myocytes PNAS, December 8, 1998; 95(25): 15096 - 15101. [Abstract] [Full Text] [PDF]

				S. O. Marx, J. Gaburjakova, M. Gaburjakova, C. Henrikson, K. Ondrias, and A. R. Marks Coupled Gating Between Cardiac Calcium Release Channels (Ryanodine Receptors) Circ. Res., June 8, 2001; 88(11): 1151 - 1158. [Abstract] [Full Text] [PDF]