What is the most accurate way to study the active properties of bladder smooth muscle?
There is often disagreement over the optimal method by which to study the active properties of smooth muscle. While some favor setting smooth muscle strips at a resting or passive tension of 1 g, others have argued in favor of determining the Lo or optimal length for maximal force generation for each individual strip. Setting each strip to its individual Lo is tedious, especially if one is dealing with multiple strips during one experiment. Is it possible to study smooth muscle strips at an average length at which most strips of similar dimensions exhibit their maximal force, and if this method is used to what extent does it underestimate the maximal force generated? When comparing bladder, smooth muscle strips 1 cm long from pregnant versus virginal rabbits, the average length at which maximal force was generated was 2.41 and 2.45 cm, respectively (p = n.s.). Studying all strips at a length of 2.5 cm (2.5 x the slack length) would have resulted in a 10% underestimate of the maximal force within each group (p = n.s.). We conclude that comparative bladder smooth muscle strip studies can be accurately carried out at an average fixed length provided that preliminary studies are done to determine the length-tension relationships for the specific experimental situation.
Zderic
S A
SA
Urology Research Laboratories, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine 19104.
Liu
G H
GH
Haab
J P
JP
Monson
F C
FC
Gong
C
C
Levin
R M
RM
D000818:Animals; D005260:Female; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D011247:Pregnancy; D011817:Rabbits; D001743:Urinary Bladder / Q000502:physiology*