The data
1.3 MB
This movie shows calcium transients within smooth muscle cells when the artery is exposed to a low concentration of noradrenaline, just when it starts to develop tone. The muscle cells are the spindle-shaped horizontal structures in various shades of green, yellow and orange. The more reddish they are, the higher their calcium concentration (the cells have been stained with calcium green-1; the images have been given pseudo-colour to enhance the apparent contrast, the real images are monochrome). The vertical structures you see shining through in the background are the intramural nerves.
Initially, there are uncoordinated calcium transients in several cells - note that they are going in different directions at different times. All of a sudden, all cells become synchronized, all calcium changes come into phase, and the tissue starts to contract.
Note: the movie has been compressed in time. The real time for these events is 2 min. 40 sec.
187 KB
This movie shows a calcium transient within a single cell in the wall of an artery stimulated with a low concentration of noradrenaline. The sequence is taken before the calcium changes become in phase. Note that the calcium transient here is like a bolus or wave sweeping along the cell from one end to the other.
Note: the movie has been expanded in time. The real time for these events is 2.7 sec.
The model
Initially, noradrenaline casues intermittent release of calcium from the sarcoplasmic reticulum (the "intracellular oscillator"). This often starts at one end of the cell, perhaps because the ratio between plasma membrane and sarcoplasmic reticulum is favourable there. The initial calcium release causes a regenerative wave of calcium release to travel along the cell. The calcium release may activate a membrane current in single cells, but this is not sufficient to significantly affect membrane potential in the functional syncytium of smooth muscle cells. Therefore individual cells are not synchronized.
When calcium release by chance occurs simultaneously in a large number of cells, the active cells together generate enough current to depolarize the membrane of all cells. This causes calcium influx, which synchronizes the cells. All cells are now in phase.
