Action potential duration and endocardial modulation of myocardial contraction in the ferret.

Abstract

Endocardial endothelium releases substances which modulate myocardial contraction. Selective endocardial removal abbreviates contraction by removing a contraction prolonging substance "endocardin". The aim of the study was to investigate whether changes in action potential duration underlie these contractile effects. The contractile effects of shortening the action potential were first characterised, using a potassium channel "opener" cromakalim (3 microM). Transmembrane action potentials were then recorded in isolated ferret papillary muscles before and after endocardial removal. Cromakalim-induced action potential abbreviation reduced contractile twitch duration. Endocardial removal itself however did not alter action potential duration. Endocardial modulation of cardiac contraction does not involve changes in action potential duration.