Changes in length and volume of smooth muscle cells of the hypertrophied rat urinary bladder

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Abstract
Rat urinary bladders were denervated by bilateral excision of the pelvic ganglion. After 10 days the hypertrophied bladders were removed, filled with 0.75 ml Krebs solution, fixated and embedded for electron microscopy. Normal bladders filled with the same volume were used as controls. Tangential and transverse sections of longitudinal muscle bundles were cut both for phase contrast and electron microscopy. The profiles of cross‐sectioned cells from control bladders had regular, often almost circular contours, and were rather uniform in size. The cell contours from the denervated bladders were irregular with wrinkled surfaces and the cells varied considerably in size. In tangential sections the cells from denervated bladders had corrugated surfaces in contrast to the control cells. Mean length and volume of the muscle cells were determined morphometrically. Whereas cell volume was larger in denervated (3 800 μm3) than in control bladders (2 200 μ3), cell length was less (226 versus 335 μm). The finding of shorter cells in denervated bladders favour the opinion, brought forward previously (Ekström & Uvelius 1981), that the rightward shift of the active length‐tension curve in denervated bladders is due to an increase in the number of muscle cells that are coupled in series around the bladder circumference.