Axial stretch of rat single ventricular cardiomyocytes causes an acute and transient increase in Ca2+ spark rate.
We investigate acute effects of axial stretch, applied by carbon fibers (CFs), on diastolic Ca2+ spark rate in rat isolated cardiomyocytes. CFs were attached either to both cell ends (to maximize the stretched region), or to the center and one end of the cell (to compare responses in stretched and nonstretched half-cells). Sarcomere length was increased by 8.01+/-0.94% in the stretched cell fraction, and time series of XY confocal images were recorded to monitor diastolic Ca2+ spark frequency and dynamics. Whole-cell stretch causes an acute increase of Ca2+ spark rate (to 130.7+/-6.4%) within 5 seconds, followed by a return to near background levels (to 104.4+/-5.1%) within 1 minute of sustained distension. Spark rate increased only in the stretched cell region, without significant differences in spark amplitude, time to peak, and decay time constants of sparks in stretched and nonstretched areas. Block of stretch-activated ion channels (2 micromol/L GsMTx-4), perfusion with Na+/Ca2+-free solution, and block of nitric oxide synthesis (1 mmol/L L-NAME) all had no effect on the stretch-induced acute increase in Ca2+ spark rate. Conversely, interference with cytoskeletal integrity (2 hours of 10 micromol/L colchicine) abolished the response. Subsequent electron microscopic tomography confirmed the close approximation of microtubules with the T-tubular-sarcoplasmic reticulum complex (to within approximately 10(-8)m). In conclusion, axial stretch of rat cardiomyocytes acutely and transiently increases sarcoplasmic reticulum Ca2+ spark rate via a mechanism that is independent of sarcolemmal stretch-activated ion channels, nitric oxide synthesis, or availability of extracellular calcium but that requires cytoskeletal integrity. The potential of microtubule-mediated modulation of ryanodine receptor function warrants further investigation.
Iribe
Gentaro
G
University of Oxford, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, United Kingdom.
Ward
Christopher W
CW
Camelliti
Patrizia
P
Bollensdorff
Christian
C
Mason
Fleur
F
Burton
Rebecca A B
RA
Garny
Alan
A
Morphew
Mary K
MK
Hoenger
Andreas
A
Lederer
W Jonathan
WJ
Kohl
Peter
P
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003078:Colchicine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels / Q000037:antagonists & inhibitors; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D018715:Microscopy, Video / Q000379:methods; D008870:Microtubules / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013111:Spider Venoms / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology
D004791:Enzyme Inhibitors; D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels; C411249:MTx4 protein, Grammostola spatulata; D010455:Peptides; D019837:Ryanodine Receptor Calcium Release Channel; D013111:Spider Venoms; D050257:Tubulin Modulators; D009569:Nitric Oxide; D012964:Sodium; D003078:Colchicine; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester