Stretch induced accumulation of total Ca and Na in cytosol and nucleus: a comparison between cardiac trabeculae and isolated myocytes.
By means of electron probe microanalysis (EPMA), we quantified changes in total sodium [Na] and calcium [Ca] concentration owing to the following: (i) local axial stretch (LAS) of isolated rat myocytes and (ii) end-to-end stretch (ETES) of rat ventricular trabeculae. For LAS, the distance between patch pipette and a cell-attached stylus was increased by maximally 20%; this activated a nonselective cationic current I(SAC) of approximately -0.5 nA, which was blocked by streptomycin. Trabeculae were stretched end-to-end from 85% L(max) to L(max). Stretch increased cytosolic [Na](total) by 34% in isolated myocytes (p < 0.001) and by 43% in trabeculae (p < 0.001). The increment in nuclear [Na](total) was 21% in myocytes (p < 0.01) and 20% in trabeculae (p < 0.001). Stretch increased [Ca](total) in isolated myocytes, in both cytosol (from 0.63 +/- 0.09 to 1.09 +/- 0.20 mmol/L, p < 0.05) and nucleus (from 0.33 +/- 0.05 to 0.64 +/- 0.13 mmol/L, p < 0.05). In trabeculae, the stretch-induced increment of 51% in cytosolic [Ca](total) remained nonsignificant (p < 0.15). In the nucleus, [Ca](total) did not change. We interpret the difference of stretch on nuclear calcium in myocytes vs. trabeculae with the assumption that LAS, but not ETES, produces shear-stress components that translate the mechanical stimulus deeply into the cell where it may modulate [Ca](total) by signals independent of I(SAC).
Wilhelm
J
J
Julius Bernstein Institute of Physiology, University of Halle, Germany.
Kondratev
D
D
Christ
A
A
Gallitelli
M F
MF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*
D012964:Sodium; D002118:Calcium