Published online before print July 18, 2002, doi: 10.1161/01.RES.0000030180.06028.23
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© 2002 American Heart Association, Inc.
Cellular Biology |
Na+-Ca2+ Exchange Activity Is Localized in the T-Tubules of Rat Ventricular Myocytes
From the School of Biomedical Sciences, University of Leeds, Leeds, UK.
Correspondence to C.H. Orchard, School of Biomedical Sciences, University of Leeds, Leeds LS2 9NQ, UK. E-mail c.h.orchard@ leeds.ac.uk
Detubulation of rat ventricular myocytes has been used to investigate the role of the t-tubules in Ca2+ cycling during excitation-contraction coupling in rat ventricular myocytes. Ca2+ was monitored using fluo-3 and confocal microscopy. In control myocytes, electrical stimulation caused a spatially uniform increase in intracellular [Ca2+] across the cell width. After detubulation, [Ca2+] rose initially at the cell periphery and then propagated into the center of the cell. Application of caffeine to control myocytes resulted in a rapid and uniform increase of intracellular [Ca2+]; the distribution and amplitude of this increase was the same in detubulated myocytes, although its decline was slower. On application of caffeine to control cells, there was a large, rapid, and transient rise in extracellular [Ca2+] as Ca2+ was extruded from the cell; this rise was significantly smaller in detubulated cells, and the remaining increase was blocked by the sarcolemmal Ca2+ ATPase inhibitor carboxyeosin. The treatment used to produce detubulation had no significant effect on Ca2+ efflux in atrial cells, which lack t-tubules. Detubulation of ventricular myocytes also resulted in loss of Na+-Ca2+ exchange current, although the density of the fast Na+ current was unaltered. It is concluded that Na+-Ca2+ exchange function, and hence Ca2+ efflux by this mechanism, is concentrated in the t-tubules, and that the concentration of Ca2+ flux pathways in the t-tubules is important in producing a uniform increase in intracellular Ca2+ on stimulation.
Key Words: t-tubules • calcium • sodium-calcium exchanger
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