['The aim was to determine the effect and mechanisms by which myocyte stretch interacts with the prolongation of action potential duration (APD) by the class III antiarrhythmic agent E-4031.', 'Action potentials and whole-cell currents were measured in isolated guinea pig ventricular myocytes with a patch clamp procedure during perfusion of normotonic, normotonic with addition of E-4031, and hypotonic plus E-4031 solutions.', 'Cell swelling leading to membrane stretch of myocytes in the whole-cell recording configuration occurred with hypotonic solution perfusion. APD, prolonged by E-4031, was reduced to less than control value with hypotonic-induced stretch. Evaluation of whole-cell currents after hypotonic-induced stretch revealed no significant changes in the L-type Ca2+ current, inward rectifier K+ current or the rapid component of the delayed rectifier K+ current. The slow component of the delayed rectifier K+ current (IKs) was upregulated and a stretch-induced CI- current was activated in hypotonic solutions. The hypotonic-induced modulation of these currents was not effected by protein kinase A or C inhibition.'] Does hypotonic-induced stretch counteract the efficacy of the class III antiarrhythmic agent E-4031 in guinea pig myocytes?