Series elasticity of urinary bladder smooth muscle.

Loops of rat bladder were stretched between pins in vitro, supported by a clamp that could be suddenly shortened by activation of a solenoid to achieve a quick release of tension. The series elasticity measured in this fashion was found to follow an exponential course and to be modified by the rate of release, indicating a minor viscous component. Tissue length decreased and series elastic stiffness appeared to increase with muscle contraction, but no alteration in series elasticity was evident when the data were related to the tension existing in the tissue at the moment of quick release. Inactivation of the contractile system by removing calcium ion with ethylene glycol-bis-(beta-aminoethylether)-N,N'-tetraacetate (EGTA) similarly did not alter series elasticity when it was related to the tension existing in the tissue. Series elasticity during the stress relaxation following a stretch, and during the contracting and relaxing phases of rhythmic contractions, was also determined by tissue tension. The conclusion drawn is that contractile cross bridges do not contribute to the series elasticity measured in bladder tissue.