Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA027

Poster Communications

Calcium signaling in epicardial and endocardial ventricular myocytes from streptozotocin - induced diabetic rat

F. C. Howarth1, L. Al Kury3, V. Sydorenko2, M. Smail1, A. Qureshi1, A. Shmygol1, J. Singh4

1. Physiology, UAE University, Al ain, United Arab Emirates. 2. Bogomoletz Institute of Physiology, Kiev, Ukraine. 3. Zayed University, Abu Dhabi, United Arab Emirates. 4. University of Central Lancashire, Preston, United Kingdom.

Diabetes mellitus (DM) is a serious global health problem and cardiovascular complications are the major cause of morbidity and mortality in diabetic patients. Electrical and mechanical function is frequently compromised in the diabetic heart. Whilst much is known about the effects of DM on contraction and Ca2+ signaling in myocytes from whole ventricle much less is known about the transmural effects of DM in the ventricle. The aim of this project was to investigate the regional effects of DM on Ca2+ signaling in epicardial (EPI) and endocardial (ENDO) myocytes from the left ventricle of streptozotocin (STZ) - induced diabetic rat. Ethical approval was obtained from the UAE University Animal Research Ethics Committee. Diabetes was induced in adult male rats with a single intraperitoneal injection of STZ/citrate buffer (60 mg/kg body weight). Age-matched controls received citrate buffer alone. Experiments were performed after 5 months of treatment. EPI and ENDO myocytes were isolated by enzyme and mechanical dispersal techniques. L-type Ca2+ current (ICa,L) and intracellular Ca2+ were simultaneously measured in fura-2 loaded myocytes by whole-cell patch clamp and fluorescence photometry. Na+/Ca2+ (NCX) current was measured in separate experiments by whole-cell patch clamp. Experiments were performed at 35-36 °C. Data are means ± S.E.M., compared by ANOVA followed by Bonferroni-corrected t tests for multiple comparisons. Diabetes was characterized by a 5-fold increase in blood glucose. Cell capacitance was significantly (p<0.05) lower in ENDO-STZ (159.4±10.8 pF, n=17) compared to ENDO-CON (203.5±12.9 pF, n=17) myocytes. Amplitude of ICa,L was not significantly (p>0.05) altered in EPI-STZ compared to EPI-CON and in ENDO-STZ compared to ENDO-CON myocytes. However, the amplitude of the Ca2+ transient was significantly increased in EPI-STZ (0.419±0.013 RU, (fura-2 ratio units), n=13) compared to EPI-CON (0.383±0.015 RU, n=16) and in ENDO-STZ (0.459±0.014 RU, n=11) compared to ENDO-CON (0.384±0.010 RU, n=16) myocytes. Currents mediated by NCX was significantly reduced at +60 mV in EPI-STZ (1.93±0.27 pA/pF, n=17) compared to EPI-CON (4.36±0.76 pA/pF, n=17) and in ENDO-STZ (1.61±0.35 pA/pF, n=14) compared to ENDO-CON (2.74±0.22 pA/pF, n=16) myocytes. NCX was also reduced at -100 mV in EPI-STZ (0.97±0.32 pA/pF, n=14) compared to EPI-CON (3.57±0.68 pA/pF, n=17) and in ENDO-STZ (0.97±0.32 pA/pF, n=14) compared to ENDO-CON (2.40±0.35 pA/pF, n=16) myocytes. The data suggest that increased amplitude of Ca2+ transients may be associated with reduced NCX current in EPI and ENDO myocytes from STZ-induced diabetic rat.

Where applicable, experiments conform with Society ethical requirements