MEMBRANE POTENTIAL-DEPENDENT AND POTENTIAL-INDEPENDENT TENSION IN CANINE TRACHEAL MUSCLE

Abstract

The double sucrose gap apparatus was used to describe properties of electromechanical coupling in canine trachealis muscle, during infusion of elevated K+ and 5-hydroxytryptamine (5-HT). With 59 mM K+ and 5-HT, quasi-steady-state relationships of membrane depolarization and tension indicated electromechanical coupling, but for a given increase in tension much smaller membrane depolarizations were seen with 5-HT than with 59 mM K+. Evoked displacements of the membrane potential with anodal or cathodal current caused relaxations or contractions, respectively, and graded displacements resulted in graded tension changes. Reversal of 59 mM K+ membrane depolarization with long anodal current pulses resulted in nearly complete reversal of K+ tension, but reversal of 5-HT membrane depolarization caused tension reversal of only 20-40%. There was a membrane potential-independent tension with 5-HT at concentrations giving near threshold to maximal 5-HT tension.