Date of Award

11-2014

Document Type

Thesis

Degree Name

Master of Science in Medical Sciences (MSMS)

Department

Medical Education

First Advisor

Frank Chri topher Howarth

Second Advisor

Murat Ahmet Oz

Third Advisor

Saadeh Suleiman

Abstract

The prevalence of diabetes mellitus is increasing at an alarming rate worldwide. Cardiovascular (CV) disease is the major cause of morbidity and mortality in diabetic patients. The search for new treatments has led to developing alternative insulin-independent treatment strategies such as sodium/glucose co-transporter (SGLT) inhibitors. Inhibition of intestinal SGLT1 impairs dietary glucose absorption, while inhibition of renal SGLT2 promotes glucose excretion leading to calorie loss and improved glycemic control. In this study, we hypothesized that inhibiting cardiac SGLTs may alter Ca2+ mobilization in myocytes. The effects of Phlorizin (PHLOR) (non-selective SGLT1 and 2 inhibitor), Quercetin-3-O-glucoside (QUER-3-G) (selective SGLT1 inhibitor), Dapagliflozin (DAPA) (SELECTIVE SGLT2 inhibitor) on ventricular myocyte shortening and intracellular Ca2+ have been investigated in streptozotocin (STZ)-induced diabetic rats and age-matched Controls. Experiments were performed at 35-36°C after 2 months of STZ treatment. Myocyte shortening, intracellular Ca2+ and L-type Ca2+ current were measured by video edge detection in electrically-stimulated (1Hz) myocytes, by fluorescence photometry in Fura-2 loaded myocytes and by whole-cell patch clamp, respectively before and after a 5 minute application of the SGLT inhibitor (10-6M) tested. The amplitude (AMP) of shortening was significantly (P<0.05) reduced by PHLOR in STZ (84.76 ±2.91%, n=20) myocytes and Controls (83.72 ±2.65%, n=23), by QUER-3-G in STZ (79.12 ±2.28%, n=20) myocytes and Controls (76.69 ±1.92%, n=30) and by DAPA in STZ (76.58 ±1.89%, n=42) myocytes and Controls (76.68 ±2.28%, n=37). The AMP of the Ca2+ transient was significantly reduced by PHLOR in STZ (82.37 ±3.16%, n=16) myocytes and Controls (73.94 ±22%, n=21) and by QUER-3-G in STZ (73.62 ±5.83%, n=18) myocytes and Controls (78.32 ±3.54%, n=41). DAPA reduced the AMP of the Ca2+ transient significantly in STZ (71.45 ±5.35%, n=16) myocytes and modestly in Controls (92.01 ±2.72%, n=17). The AMP of L-type Ca2+ current was significantly reduced in myocytes from STZ compared to Control rats across a range of test potentials and was additionally reduced by DAPA. Myofilament sensitivity to Ca2+ and SR Ca2+ were not significantly altered by PHLOR, QUER-3-G or DAPA. The reduction in L-type Ca2+ current in the presence of DAPA may partly underlie its negative inotropic effects. However, further studies are required to investigate the mechanism(s) behind the negative inotropic effects of PHLOR and QUER-3-G.

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