Nanomechanical analysis of insulinoma cells after glucose and capsaicin stimulation using atomic force microscopy.

AIM: Glucose stimulates insulin secretion from pancreatic islet ß cells by altering ion channel activity and membrane potential in the ß cells. TRPV1 channel is expressed in the ß cells and capsaicin induces insulin secretion similarly to glucose. This study aims to investigate the biophysical properties of the ß cells upon stimulation of membrane channels using an atomic force microscopic (AFM) nanoindentation system. METHODS: ATCC insulinoma cell line was used. Cell stiffness, a marker of reorganization of cell membrane and cytoskeleton due to ion channel activation, was measured in real time using an integrated AFM nanoindentation system. Cell height that represented structural changes was simultaneously recorded along with cell stiffness. RESULTS: After administration of glucose (16, 20 and 40 mmol/L), the cell stiffness was markedly increased in a dose-dependent manner, whereas cell height was changed in an opposite way. Lower concentrations of capsaicin (1.67 × 10(-9) and 1.67 × 10(-8) mol/L) increased the cell stiffness without altering cell height. In contrast, higher concentrations of capsaicin (1.67 × 10(-6) and 1.67 × 10(-7) mol/L) had no effect on the cell physical properties. CONCLUSION: A unique bio-nanomechanical signature was identified for characterizing biophysical properties of insulinoma cells upon general or specific activation of membrane channels. This study may deepen our understanding of stimulus-secretion coupling of pancreatic islet cells that leads to insulin secretion.

Effects of simvastatin on activities of endogenous antioxidant enzymes and angiotensin-converting enzyme in rat myocardium with pressure-overload cardiac hypertrophy.

AIM: To investigate effects of simvastatin (Sim) on the activities of antioxidant enzymes and angiotensin-converting enzyme in rat myocardium with pressure-overload cardiac hypertrophy. METHODS: Left ventricular hypertrophy (LVH) was induced by partly constricting rat abdominal aorta between the left and right renal artery. Rats were given ig Sim 1.8 and 3.6 mg . kg-1 . d-1 for 8 weeks following 6 weeks aortic constriction. Activities of antioxidant enzymes and angiotensin-converting enzyme, and lipid peroxidation of left ventricular (LV) tissue were determined. RESULTS: Contents of angiotensin II and thiobarbituric acid reactive substances (TBARS), and activity of ACE in LVH group (n = 8) were increased by 163 %, 90 %, and 130 %, respectively (P < 0.01)compared with sham-operated group (n = 7), and were decreased by 30 %, 37 %, and 51 %, respectively (P < 0.01) in high dosage Sim treatment group (n = 9) compared with LVH group. Activities of catalase and glutathione peroxidase of LV tissue in LVH group were decreased by 29 % and 23 % (P < 0.01) compared with sham-operated group, and were increased by 32 % and 22 % (P < 0.01) in high dosage Sim treatment group compared with LVH group. Activity of Cu, Zn-superoxide dismutase (SOD) of LV tissue was increased by 33 % in LVH group compared with sham-operated group. Sim treatment did not significantly affect activity of Cu,Zn-SOD. CONCLUSION: Alteration of redox status in myocardium is associated with cardiac hypertrophy and inhibitory effects of Sim on cardiac hypertrophy in rats model might be linked to its antioxidant effects.