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 smoot h muscle strips at a resting or passive tension of 1 g, others have ar gued in favor of determining the L, or optimal length for maximal forc e generation for each individual strip. Setting each strip to its indi vidual L, is tedious, especially if one is dealing with multiple strip s during one experiment. Is it possible to study smooth muscle strips at an average length at which most strips of similar dimensions exhibi t their maximal force, and if this method is used to what extent does it underestimate the maximal force generated? When comparing bladder s mooth muscle strips 1 cm long from pregnant versus virginal rabbits, t he 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% underestimat e of the maximal force within each group (p = n.s.). We conclude that comparative bladder smooth muscle strip studies can be accurately carr ied out at an average fixed length provided that preliminary studies a re done to determine the length-tension relationships for the specific experimental situation.