Increase in resting tension of tracheal muscle due to rigor during metabolic inhibition

Abstract

Resting tension of canine tracheal smooth muscle increased when glucose and O2 were withdrawn from the bathing medium. Similar treatment of muscle stimulated with carbachol caused first a relaxation and then a secondary increase in tension. The increase in tension due to metabolic inhibition, unlike normal tracheal contractions, was insensitive to Ca depletion, was not associated with an active state, and was accompanied by marked reduction of tissue/ATP, creatine phosphate and glycogen content. Because muscle stiffness was also increased the hypoxic glucose-free contracture is probably due to rigor and not to an increased tissue Ca level as was previously suggested. Rigor shortening during lightly loaded isotonic conditions is better maintained than rigor tension during isometric conditions. Rigor tension is reduced irreversibly on imposition of a load and, therefore, the load-extension relationship during rigor in smooth muscle should be studied by making only small load changes.