Mechanoelectric feedback does not contribute to the Frank-Starling relation in the rat and guinea pig heart

Abstract: Mechanoelectric feedback (MEF) is the process by which mechanical forces on the myocardium can alter its electrical properties. The effect can be large enough to induce ectopic beats or fibrillation. However, the role of MEF at physiological levels of mechanical stress is not clear. We have investigated alteration in action potential morphology in rat and guinea pig ventricle and in rat atrial tissue at levels of stretch near the plateau of the Frank-Starling curve. Stretch of >100 mm.Hg End Diastolic Left Ventricular Pressure (EDLVP) or rapidly applied stretch (EDLVP increased by 25 mm.Hg within 100 ms) often triggered ectopic beats in isolated rat and guinea-pig hearts. However, ventricular epicardial monophasic action potentials (MAPs) recorded during stretch to EDLVP up to 30 mm. Hg showed no consistent changes in action potential duration (at APD20, APD50 or APD80) in either species. MAP recording detected APD prolongation with very small concentrations of 4-AP (10 μM), confirming the discrimination of the recording technique. In isolated rat atrial strips, no changes in intracellular action potential morphology or membrane potential were seen when stretched to levels producing an optimum increase in contractility. We conclude that alteration in action potential morphology with stretch does not contribute to the Frank-Starling relation in ventricle of rat or guinea-pig isolated heart, or in rat atrial tissue.