Multiple pathways responsible for the stretch-induced increase in Ca2+ concentration in toad stomach smooth muscle cells
Department of Physiology
Animals; Bufo marinus; Calcium; Calcium Channels; Membrane Potentials; Muscle Contraction; Muscle, Smooth; Patch-Clamp Techniques; Stomach
Life Sciences | Medicine and Health Sciences
1. A digital imaging microscope with fura-2 as the Ca2+ indicator was used to determine the sources for the rise in intracellular calcium concentration ([Ca2+]i) that occurs when the membrane in a cell-attached patch is stretched. Unitary ionic currents from stretch-activated channels and [Ca2+]i images were recorded simultaneously. 2. When suction was applied to the patch pipette to stretch a patch of membrane, Ca2+-permeable cation channels (stretch-activated channels) opened and a global increase in [Ca2+]i occurred, as well as a greater focal increase in the vicinity of the patch pipette. The global changes in [Ca2+]i occurred only when stretch-activated currents were sufficient to cause membrane depolarization, as indicated by the reduction in amplitude of the unitary currents. 3. When Ca2+ was present only in the pipette solution, just the focal change in [Ca2+]i was obtained. This focal change was not seen when the contribution from Ca2+ stores was eliminated using caffeine and ryanodine. 4. These results suggest that the opening of stretch-activated channels allows ions, including Ca2+, to enter the cell. The entry of positive charge triggers the influx of Ca2+ into the cell by causing membrane depolarization, which presumably activates voltage-gated Ca2+ channels. The entry of Ca2+ through stretch-activated channels is also amplified by Ca2+ release from internal stores. This amplification appears to be greater than that obtained by activation of whole-cell Ca2+ currents. These multiple pathways whereby membrane stretch causes a rise in [Ca2+]i may play a role in stretch-induced contraction, which is a characteristic of many smooth muscle tissues.
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Citation: J Physiol. 2000 Apr 1;524 Pt 1:3-17.
The Journal of physiology
Kirber, Michael T.; Guerrero-Hernandez, Agustin; Bowman, Douglas S.; Fogarty, Kevin E.; Tuft, Richard A.; Singer, Joshua J.; and Fay, Fredric S., "Multiple pathways responsible for the stretch-induced increase in Ca2+ concentration in toad stomach smooth muscle cells" (2000). Open Access Articles. 1491.