Silk suture used in standard organ bath studies contracts upon exposure to Krebs buffer

INTRODUCTION: Muscles of all types are routinely excised and studied under isometric conditions using force transducers in standard organ baths. In such studies, the muscle is stretched or "preloaded," as the magnitudes of the contractions evoked by various stimuli can vary markedly depending on this baseline parameter: many such studies refer to an optimal length and/or preload tension. While calibrating our equipment, we were surprised to find that the silk suture, which is commonly used in such studies, can generate considerable tension of its own, completely independent of any muscle tissue. METHODS: We compared two different types of silk suture in muscle baths using the standard organ bath technique, measuring baseline tension upon addition of various solvents/buffers. RESULTS: One type of silk suture was inert in that, upon stretching to a given degree, there was no important change in preload tension upon addition of bathing medium (Krebs buffer). The second type of silk suture, however, which is also widely available commercially, exhibited substantial contractile responses upon exposure to standard Krebs buffer solution, with magnitudes typically exceeding several grams force. This change developed over the first 30-60 min of exposure to Krebs, after which tension was stable. This change was not observed if the suture was presoaked for 60 min before hanging in the muscle bath, but was observed if the suture was allowed to dry again before use. Other solvents such as ethanol and DMSO did not alter tension. DISCUSSION: While this property of silk suture may be well known in the surgical setting, it is less well appreciated by other users of this material. This phenomenon is of major importance to any experimental study of muscle function, as it alters the preload tension under which such studies are carried out.