Na+-Ca2+ exchange activity is localized in the T-tubules of rat ventricular myocytes.
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.
Yang
Z
Z
School of Biomedical Sciences, University of Leeds, Leeds, UK.
Pascarel
C
C
Steele
D S
DS
Komukai
K
K
Brette
F
F
Orchard
C H
CH
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D021961:Cell Membrane Structures / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002469:Cell Separation; D025802:Electric Capacitance; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D005559:Formamides / Q000494:pharmacology; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007424:Intracellular Fluid / Q000378:metabolism; D018613:Microscopy, Confocal; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D009532:Nickel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000201:enzymology; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*
D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D005559:Formamides; D019831:Sodium-Calcium Exchanger; D002110:Caffeine; C031066:formamide; D009532:Nickel; D000251:Adenosine Triphosphatases; D002118:Calcium