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 ISAC of approximately –0.5 nA, which was blocked by streptomycin. Trabeculae were stretched end-to-end from 85% Lmax to Lmax. 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 ISAC.
Depletion of intracellular Ca2+ stores activates a maitotoxin-sensitive nonselective cationic current in beta-cells.