Contraction and Intracellular Calcium Transport in Epicardial and Endocardial Ventricular Myocytes from Streptozotocin-Induced Diabetic Rat

Abstract

Diabetes mellitus (DM) is a global health problem. According to the International Diabetes Federation, 424.9 million people suffered from DM in 2017 and this number is expected to rise to 628.6 million by 2045. Although diabetes can affect every organ in the body, cardiovascular disease is a major cause of death and disability in people with diabetes. Diabetic patients frequently suffer from systolic and diastolic dysfunction. Within the ventricles, the electromechanical properties of cardiac myocytes vary transmurally. The aim of this study was to investigate contraction and Ca2+ transport in epicardial (EPI) and endocardial (ENDO) myocytes from the left ventricle in the streptozotocin (STZ)-induced diabetic rat heart. Experiments were performed 5–6 months after STZ treatment. Ventricular myocytes were isolated by enzymic and mechanical dispersal
techniques from EPI and ENDO regions of the left ventricle. Contraction and free intracellular Ca2+ concentration (Ca2+)i were measured by video edge detection and fl uorescence photometry techniques, respectively. Myocyte length and calculated surface area were smaller in EPI-STZ compared to EPI-CON. Time to peak (TPK) shortening was prolonged in EPI-STZ compared to EPI-CON and in ENDO-STZ compared to ENDO-CON myocytes. Time to half (THALF) relaxation of shortening was prolonged in EPI-STZ compared to EPI-CON. TPK Ca2+ transient was prolonged in EPI-STZ compared to EPI-CON, ENDO-STZ compared to ENDO-CON, ENDO-STZ compared to EPI-STZ and in ENDO-CON compared to EPI-CON myocytes. THALF decay of the Ca2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. Fractional release of Ca2+ was increased in ENDO-STZ compared to ENDO-CON and in ENDO-STZ compared to EPI-STZ. Recovery of the
Ca2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. In conclusion, the kinetics of contraction and Ca2+ transient, fractional release of Ca2+ from the sarcoplasmic reticulum are altered to different extents in EPI and ENDO myocytes from STZ-induced diabetic rat.