Cytosolic Ca 2+ concentration and pH of diabetic rat myocytes during metabolic inhibition

Abstract

To investigate the role of Ca 2+ metabolism and pH in diabetic cardiomyopathy, intracellular Ca 2+ concentration ([Ca 2+]i) and intracellular pH (pHi) of isolated myocytes were measured simultaneously using fura-2 and BCECF. We used diabetic (D.M.) rats at 8 weeks after the injection of streptozotocin (45 mg/kg, i.v.). (1) [Ca 2+]i of D.M. myocytes was lower than that of controls (53 ± 3 and 75 ± 5 n m, mean ± S.E., P<0.01). There was no difference in pHi (7.06 ± 0.02 in D.M., 7.07 ± 0.02 in control). There was no difference in the percentage of non-rounded cells at 30 min after the perfusion of glucose-free solution which contained 2 m m sodium cyanide (NaCN) between D.M. and controls (53% and 52%). When cells were rounded, the value of [Ca 2+]i was significantly lower in D.M. myocytes than that in controls (172 ± 21 and 421 ± 106 n m, P<0.05). (2) When the cells were shortened or rounded in the high [Ca 2+]o solution (24.5 m m), [Ca 2+]i of D.M. rats was significantly lower than that of control rats. (3) The percentage of non-rounded cells at 30 min after the perfusion of NaCN increased in controls by 50 m m glucose (95%, P<0.01), but not in D.M. (47%). Insulin (25 mU/ml) and glucose (15 m m) increased the percentage of non-rounded cells in D.M. after 30 min perfusion with NaCN (88%, P<0.01 v.s. 53% without glucose nor insulin). It is suggested that there are disturbances of Ca 2+ metabolism in D.M. myocytes, and that there is a close relation between cell injury and glucose utilization during metabolic inhibition.