J P Ward1. 1. Department of Medicine, United Medical School, London.
Abstract
STUDY OBJECTIVE: The aim was to investigate a possible defect in cardiac muscle contractile performance following chronic K+ depletion. DESIGN: Cardiac muscle force development, membrane potential, and action potential configuration were measured in isolated superfused right ventricular papillary muscles or trabeculae from control or K+ depleted NZW rabbits. The effects of adrenaline, strophanthidin, and changes in external [Ca2+] and [K+] were investigated. EXPERIMENTAL MATERIALS: Experiments were performed on 50 adult NZW rabbits, average weight 2.3 kg, which were fed either a control diet (n = 25), or a K+ deficient diet (n = 25) for 25 d. MEASUREMENTS AND MAIN RESULTS: There was a significant reduction in contractile force in preparations from the K+ depleted group compared to those from control animals. This was associated with an increased positive inotropic response to low [K+], but an apparent reduction in response to adrenaline. There was no significant difference between groups as to the effect of strophanthidin. CONCLUSIONS: It is suggested that the reduction in response to adrenaline reflects a down regulation in beta receptor density, due to an increased level of circulating catecholamines, and that the defect in myocardial function is a result of adaptive changes to Ca2+ handling mechanisms within the cell.
STUDY OBJECTIVE: The aim was to investigate a possible defect in cardiac muscle contractile performance following chronic K+ depletion. DESIGN: Cardiac muscle force development, membrane potential, and action potential configuration were measured in isolated superfused right ventricular papillary muscles or trabeculae from control or K+ depleted NZW rabbits. The effects of adrenaline, strophanthidin, and changes in external [Ca2+] and [K+] were investigated. EXPERIMENTAL MATERIALS: Experiments were performed on 50 adult NZW rabbits, average weight 2.3 kg, which were fed either a control diet (n = 25), or a K+ deficient diet (n = 25) for 25 d. MEASUREMENTS AND MAIN RESULTS: There was a significant reduction in contractile force in preparations from the K+ depleted group compared to those from control animals. This was associated with an increased positive inotropic response to low [K+], but an apparent reduction in response to adrenaline. There was no significant difference between groups as to the effect of strophanthidin. CONCLUSIONS: It is suggested that the reduction in response to adrenaline reflects a down regulation in beta receptor density, due to an increased level of circulating catecholamines, and that the defect in myocardial function is a result of adaptive changes to Ca2+ handling mechanisms within the cell.