Alloxan-induced diabetes reduces sarcolemmal Na⁺-K⁺ pump function in rabbit ventricular myocytes

Abstract

The effect of diabetes on sarcolemmal Na(+)-K(+) pump function is important for our understanding of heart disease associated with diabetes and design of its treatment. We induced diabetes characterized by hyperglycemia but no other major metabolic disturbances in rabbits. Ventricular myocytes isolated from diabetic rabbits and controls were voltage clamped and internally perfused with the whole cell patch-clamp technique. Electrogenic Na(+)-K(+) pump current (I(p), arising from the 3:2 Na(+)-to-K(+) exchange ratio) was identified as the shift in holding current induced by Na(+)-K(+) pump blockade with 100 micromol/l ouabain in most experiments. There was no effect of diabetes on I(p) recorded when myocytes were perfused with pipette solutions containing 80 mmol/l Na(+) to nearly saturate intracellular Na(+)-K(+) pump sites. However, diabetes was associated with a significant decrease in I(p) measured when pipette solutions contained 10 mmol/l Na(+). The decrease was independent of membrane voltage but dependent on the intracellular concentration of K(+). There was no effect of diabetes on the sensitivity of I(p) to extracellular K(+). Pump inhibition was abolished by restoration of euglycemia or by in vivo angiotensin II receptor blockade with losartan. We conclude that diabetes induces sarcolemmal Na(+)-K(+) pump inhibition that can be reversed with pharmacological intervention.

Reduced Na+ current density underlies impaired propagation in the diabetic rabbit ventricle

“…6C). Further, it has been suggested that the Na + -K + pump function is impaired in diabetes [20]. To assess its potential impact, we reduced the Na + /K + pump current in the model by 30%.…”

“…Diabetes was induced using techniques adapted from published studies [13–15, 20]. A single injection of alloxan monohydrate (140–160 mg/kg body weight) was administered, via the ear vein during brief sedation (via a combination of ketamine/xylazine).…”

Effect of ouabain on metabolic oxidative state in living cardiomyocytes evaluated by time-resolved spectroscopy of endogenous NAD(P)H fluorescence

“…We have previously demonstrated 11 that a switch in the use of these substrates is highly important in certain physiological conditions, such as physiological and pathological pregnancy, which are also characterized by increased levels of endogenous ouabain. 35 This result can be of importance also in other pathological conditions as the sodium pump is regulated in conditions such as hyperglycemia associated with diabetes, 36 and is linked to mediation of the glucose uptake and/or lactate production. Na þ ∕K þ -ATPase was shown to interact with multiple signaling proteins to transmit ouabain signals, 3,37 and several intracellular pathways are known to be implicated in this transmission; namely, ouabain was shown to affect mitochondrial NAD(P)H and ROS generation.…”

Angiotensin II inhibits the Na+-K+ pump via PKC-dependent activation of NADPH oxidase

“…Although this study was performed on patch-clamped, internally perfused myocytes, our previous studies indicate that ANG II also inhibits the pump in isolated intact myocytes and in vivo (17,19,20). We treated rabbits with an angiotensinconverting enzyme inhibitor (ACEI) or an ANG II type I receptor (AT 1 ) antagonist for 1 wk, isolated myocytes, and measured I p .…”