CELL LENGTH MEASUREMENTS IN LONGITUDINAL SMOOTH-MUSCLE STRIPS OF THE PIG URINARY-BLADDER

In this study the length of smooth muscle cells in muscle bundles of p ig urinary bladder wall was determined after dissection in Tyrode buff ers with different calcium concentrations (Ca2+!). Previous studies h ave shown that the length of isolated smooth muscle cells decreases wi th an increase in Ca2+! in the buffer. Unlike the results in isolated cells, no significant differences in length were found between cells in strips subjected to different Ca2+!. Cells in bundles dissected fr om filled bladders were significantly larger than those dissected from emptied bladders. Cells in strips from emptied bladders dissected in 1.8 mM Ca2+-Tyrode buffer were shorter than those obtained in Ca2+-fre e buffer. From the measurements it was concluded that: (1) Cell length in intact tissue is directly related to tissue length; series elastic structures external to the cells do not allow significant shortening of the cells. (2) Passive parallel elasticity outside the cells accoun ts for passive shortening when bladders are emptied manually. (3) Cell length is not related to empty bladder weight. (4) A positive relatio n exists between empty bladder weight and bladder capacity.