Intracellular protons inhibit transient outward K+ current in ventricular myocytes from diabetic rats

1996 ◽  
Vol 271 (5) ◽  
pp. H2154-H2161 ◽  
Author(s):  
Z. Xu ◽  
K. P. Patel ◽  
G. J. Rozanski
Keyword(s):  
Ventricular Myocytes ◽  
External Solution ◽  
Cell Voltage ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Intracellular Acidosis ◽  
K Current ◽  
Acid Load ◽  
Dimethyl Amiloride ◽  
And Control

This study examined the effects of protons on cardiac ion channel function in early stages of diabetes mellitus. Transient outward (I(to)) and inward rectifier K+ (IK1) currents were recorded by the whole cell, voltage-clamp technique in ventricular myocytes isolated from hearts of streptozotocin-induced diabetic and control rats. Proton concentration was controlled by independently varying the pH of buffered external or pipette (pHp) solutions. External acidification did not alter I(to) in diabetic rat myocytes when initiated after intracellular dialysis with standard pHp 7.2, but when these cells were dialyzed with acidic pHp (6.6 or 6.0), I(to) density was significantly reduced. Low pHp also reduced I(to) density more in cells from diabetic rats than in controls, whereas alkaline pHp had no effect on either group of cells compared with standard pHp 7.2. In control myocytes dialyzed with pHp 6.0, block of Na+/H+ exchange with 5-(N,N-dimethyl)-amiloride (DMA) or Na(+)-free external solution further reduced I(to) density compared with pHp 6.0 alone, whereas these treatments had less effect on acid-dialyzed cells from diabetic rats. Dialysis with pHp to 6.0 did not alter IK1 in either group of cells compared with standard pHp 7.2, but when done in the presence of DMA or Na(+)-free conditions, IK1 density in both groups was significantly reduced by nearly the same amount. We conclude that intracellular protons inhibit I(to) channels in ventricular myocytes from diabetic and control rats, but that for a given acid load, inhibition is markedly greater in diabetics. This difference may be explained by a diabetes-induced decrease in Na+/H+ exchange that limits proton extrusion during intracellular acidosis. Moreover, acidosis may differentially suppress I(to) and IK1, suggesting that these K+ channels exhibit dissimilar sensitivities to intracellular protons.

Metabolic basis of decreased transient outward K+ current in ventricular myocytes from diabetic rats

1996 ◽  
Vol 271 (5) ◽  
pp. H2190-H2196 ◽  
Author(s):  
Z. Xu ◽  
K. P. Patel ◽  
G. J. Rozanski
Keyword(s):  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Diabetic Rats ◽  
K Channel ◽  
Diabetic Rat ◽  
Channel Function ◽  
Early Stages ◽  
Metabolic Basis ◽  
External Glucose

The purpose of this study was to examine the mechanisms of alterations in cardiac K+ channel function in early stages of experimental diabetes mellitus induced by streptozotocin. Transient outward (Ito) and inward rectifier (IK1) K+ currents were recorded by the whole cell voltage-clamp technique in ventricular myocytes isolated from hearts of 2- to 4-wk diabetic and age-matched control rats. Ito density in myocytes from diabetic rats was approximately 30% less than control (at +60 mV; P < 0.01) under basal recording conditions in the presence of 18 mM external glucose, whereas IK1 density was not different between groups. When external glucose concentration was decreased to 5 mM for 4-6 h, basal Ito density was not changed in either group of myocytes. To further examine the possible metabolic basis of reduced Ito density in myocytes from diabetic rats, we separately tested three structurally different compounds that affect substrate utilization in cardiac myocytes: insulin (0.1 microM), dichloroacetate (1.5 mM), and L-carnitine (10 mM). Each compound completely normalized Ito density in myocytes from diabetic rats treated in vitro for 4-6 h. The same agents had no effect on Ito density in control myocytes, nor was IK1 altered in either group of cells. These data provide the first evidence to support the hypothesis that there is a metabolic basis for decreased Ito density in diabetic rat ventricular myocytes in early stages of this model. Furthermore, our data suggest that depressed glucose metabolism in the diabetic heart may be a key factor underlying changes in Ito channel function, because agents that increase glucose utilization normalize Ito density within a short time period.

scholarly journals Facilitated Ca2+ homeostasis and attenuated myocardial autophagy contribute to alleviation of diabetic cardiomyopathy after bariatric surgery

2018 ◽  
Vol 315 (5) ◽  
pp. H1258-H1268 ◽  
Author(s):  
Xin Huang ◽  
Shaozhuang Liu ◽  
Dong Wu ◽  
Yugang Cheng ◽  
Haifeng Han ◽  
...  
Keyword(s):  
Bariatric Surgery ◽  
Diabetic Cardiomyopathy ◽  
Ventricular Myocytes ◽  
Mammalian Target Of Rapamycin ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Autophagic Flux ◽  
Fk506 Binding Protein ◽  
Plasmic Reticulum ◽  
Chloroquine Treatment

Bariatric surgery has been reported to relieve diabetic cardiomyopathy (DCM) effectively. However, the mechanisms remain largely unknown. To determine the effects of bariatric surgery on DCM via modulation of myocardial Ca2+ homeostasis and autophagy, sleeve gastrectomy (SG), duodenal-jejunal bypass (DJB), and sham surgeries were performed in diabetic rats induced by high-fat diet and a low dose of streptozotocin. Cardiac remodeling was assessed by a series of morphometric and histological analyses. Transthoracic echocardiography and hemodynamic measurements were performed to determine cardiac function. Ca2+ homeostasis was evaluated by measuring Ca2+ transients with fura-2 AM in isolated ventricular myocytes along with detection of the abundance of Ca2+ regulatory proteins in the myocardium. Myocardial autophagic flux was determined by expression of autophagy-related proteins in the absence and presence of chloroquine. Both SG and DJB surgery alleviated DCM morphologically and functionally. Ca2+ transients exhibited a significantly higher amplitude and faster decay after SG and DJB, which could be partially explained by increased expression of ryanodine receptor 2, sarco(endo)plasmic reticulum Ca2+-2ATPase, 12.6-kDa FK506-binding protein, and hyperphosphorylation of phospholamban. In addition, a lower level of light chain 3B and higher level of p62 were detected after both SG and DJB, which was not reversed by chloroquine treatment and associated with activated mammalian target of rapamycin and attenuated AMP-activated protein kinase signaling pathway. Collectively, these results provided evidence that bariatric surgery could alleviate DCM effectively, which may result, at least in part, from facilitated Ca2+ homeostasis and attenuated autophagy, suggesting a potential choice for treatment of DCM when properly implemented. NEW & NOTEWORTHY The present study is the first to investigate the modulation of myocardial Ca2+ homeostasis and autophagy after bariatric surgery and to examine its effects on diabetic cardiomyopathy. Bariatric surgery could facilitate myocardial Ca2+ homeostasis and attenuate myocardial autophagy, contributing to the alleviation of cardiomyopathy morphologically and functionally in a diabetic rat model.

Differential modulation by adenylate cyclase of Ca2+ and delayed K+ current in ventricular myocytes

1994 ◽  
Vol 266 (4) ◽  
pp. H1551-H1557 ◽  
Author(s):  
K. Harada ◽  
T. Iijima
Keyword(s):  
Adenylate Cyclase ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Threshold Concentration ◽  
Water Soluble ◽  
Delayed Rectifier ◽  
Differential Modulation ◽  
Beta Adrenoceptor ◽  
Ventricular Cells ◽  
K Current

This study was designed to investigate the differential modulation of the L-type Ca2+ (ICa) and the delayed rectifier K+ (IK) currents by direct activation of adenylate cyclase in guinea pig ventricular preparations. Action potentials were measured with conventional microelectrodes in excised papillary muscles. Isoproterenol significantly shortened the action potential duration at 90% repolarization (APD90) at 0.1 nM but significantly prolonged it at a higher concentration (10 nM). A water-soluble forskolin derivative, 6-(3-dimethylaminopropionyl) forskolin (NKH-477), slightly but significantly shortened APD at 12 nM but not at a higher concentration (120 nM). Effects of isoproterenol and NKH-477 on ICa and IK were also investigated by use of the whole cell voltage-clamp technique in single ventricular cells. Isoproterenol increased not only IK but also ICa at the same threshold concentration (0.3 nM). In contrast, the threshold concentration of NKH-477 for increasing IK (approximately 1 nM) was clearly lower than that for increasing ICa (10 nM). These results indicate that ICa and IK channels could be differentially regulated during beta-adrenoceptor stimulation.

scholarly journals Effects of Type II diabetes on exercising skeletal muscle blood flow in the rat

2010 ◽  
Vol 109 (5) ◽  
pp. 1347-1353 ◽  
Author(s):  
Steven W. Copp ◽  
K. Sue Hageman ◽  
Brad J. Behnke ◽  
David C. Poole ◽  
Timothy I. Musch
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Type Ii Diabetes ◽  
Blood Glucose Concentration ◽  
Muscle Blood Flow ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Type Ii ◽  
The Individual ◽  
And Control

The purpose of the present investigation was to examine the muscle hyperemic response to steady-state submaximal running exercise in the Goto-Kakizaki (GK) Type II diabetic rat. Specifically, the hypothesis was tested that Type II diabetes would redistribute exercising blood flow toward less oxidative muscles and muscle portions of the hindlimb. GK diabetic ( n = 10) and Wistar control ( n = 8, blood glucose concentration, 13.7 ± 1.6 and 5.7 ± 0.2 mM, respectively, P < 0.05) rats were run at 20 m/min on a 10% grade. Blood flows to 28 hindlimb muscles and muscle portions as well as the abdominal organs and kidneys were measured in the steady state of exercise using radiolabeled 15-μm microspheres. Blood flow to the total hindlimb musculature did not differ between GK diabetic and control rats (161 ± 16 and 129 ± 15 ml·min−1·100g−1, respectively, P = 0.18). Moreover, there was no difference in blood flow between GK diabetic and control rats in 20 of the individual muscles or muscle parts examined. However, in the other eight muscles examined that typically are comprised of a majority of fast-twitch glycolytic (IIb/IIdx) fibers, blood flow was significantly greater (i.e., ↑31–119%, P < 0.05) in the GK diabetic rats. Despite previously documented impairments of several vasodilatory pathways in Type II diabetes these data provide the first demonstration that a reduction of exercising muscle blood flow during submaximal exercise is not an obligatory consequence of this condition in the GK diabetic rat.

Tedisamil inactivates transient outward K+ current in rat ventricular myocytes

1989 ◽  
Vol 257 (5) ◽  
pp. H1746-H1749 ◽  
Author(s):  
I. D. Dukes ◽  
M. Morad
Keyword(s):  
Ventricular Myocytes ◽  
Sodium Current ◽  
Outward Current ◽  
Cell Voltage ◽  
Transient Outward Current ◽  
Dependent Manner ◽  
Rat Ventricular Myocytes ◽  
K Current ◽  
New Type ◽  
Inwardly Rectifying

The action of tedisamil, a new bradycardiac agent with antiarrhythmic properties, was investigated in single rat ventricular myocytes using the whole cell voltage-clamp technique. Under current clamp conditions, 1-20 microM tedisamil caused marked prolongations of the action potential. Over the same concentration range, in voltage-clamped myocytes, tedisamil suppressed the transient outward current (ito) and enhanced its inactivation in a dose-dependent manner. The half-maximal dose for the effect of tedisamil on ito was approximately 6 microM. Tedisamil had no significant effects on the inwardly rectifying potassium current and calcium current but did suppress the sodium current at concentrations greater than 20 microM. Our findings suggest that tedisamil represents a new type of antiarrhythmic agent that primarily suppresses the transient outward K+ current.

Mitochondrial dysfunction accompanies diastolic dysfunction in diabetic rat heart

1996 ◽  
Vol 271 (1) ◽  
pp. H192-H202 ◽  
Author(s):  
C. E. Flarsheim ◽  
I. L. Grupp ◽  
M. A. Matlib
Keyword(s):  
Atp Synthesis ◽  
Insulin Dependent Diabetes Mellitus ◽  
Work Load ◽  
Diabetic Rats ◽  
Dependent Diabetes Mellitus ◽  
Diabetic Rat ◽  
Synthesis Rate ◽  
Insulin Dependent ◽  
And Control ◽  
Stimulation Of

The objective of this study was to determine whether a defect in mitochondrial respiratory function accompanies the development of diabetic cardiomyopathy. The hypothesis tested in this study is that a decrease in Ca2+ uptake into mitochondria may prevent the stimulation of Ca(2+)-sensitive matrix dehydrogenases and the rate of ATP synthesis. Streptozotocin (55 mg/kg)-induced diabetic rats were used as a model of insulin-dependent diabetes mellitus. Hearts from 4-wk diabetic rats had basal heart rates and rates of contraction and relaxation similar to control. Isoproterenol caused a similar increase in the rate of contraction in diabetic and control hearts, whereas the peak rate of relaxation was reduced in diabetic hearts. Mitochondrial Ca2+ uptake was reduced in mitochondria from diabetic hearts after 2 wk of diabetes. Na(+)-induced Ca2+ release was unchanged. State 3 respiration rate was depressed in mitochondria from diabetic rats only when the respiration was supported by the substrate of a Ca(2+)-regulated matrix enzyme. The pyruvate dehydrogenase activity was reduced in diabetic mitochondria compared with that of control. It was concluded that mitochondria from diabetic hearts had a decreased capacity to upregulate ATP synthesis via stimulation of Ca(2+)-sensitive matrix dehydrogenases. The impairment in the augmentation of ATP synthesis rate accompanies a decreased rate of relaxation during increased work load.

scholarly journals On the role of sodium ions in the regulation of the inward-rectifying potassium conductance in cat ventricular myocytes.

1989 ◽  
Vol 94 (2) ◽  
pp. 329-348 ◽  
Author(s):  
R D Harvey ◽  
R E Ten Eick
Keyword(s):  
Intracellular Ph ◽  
Ventricular Myocytes ◽  
Membrane Surface ◽  
Potassium Conductance ◽  
Respiratory Acidosis ◽  
Proton Exchange ◽  
Intracellular Acidosis ◽  
Patch Clamp Technique ◽  
Subsequent Decrease ◽  
K Current

The conductance of the inward-rectifying K+ current (IK1) in isolated cat ventricular myocytes is decreased by reducing the extracellular Na+ concentration. Using a whole-cell patch-clamp technique, possible mechanisms underlying this Na+ dependence were investigated. These included (a) block of inward K+ current by the Na+ substitute, (b) changes in membrane surface charge associated with removal of extracellular Na+, (c) increases of intracellular Ca2+ due to suppression of Na-Ca exchange, (d) reduction of a Na+-dependent K+ conductance due to a subsequent decrease of intracellular Na+, (e) reduction of IK1 conductance (gK1) associated with reduction of intracellular pH due to suppression of Na-proton exchange. The findings support the hypothesis that the effect of removing Na+ is mediated through a decrease in intracellular pH. These include observations that: (a) reducing internal pH by reducing external pH caused a decrease in gK1, and the conductance changes caused by reducing extracellular pH and removing extracellular Na+ were not additive: (b) the effect of reducing pHo was attenuated by dialyzing with a low pH internal solution; (c) gK1 was reduced by exposure to the Na-proton exchange inhibitor dimethylamiloride, and this effect was absent in the absence of Na+. These findings imply that physiological or pathological processes such as ischemia and metabolic or respiratory acidosis which can produce intracellular acidosis should be expected to affect K+ permeation through the IK1 channel.

scholarly journals Effects of Pioglitazone on Ventricular Myocyte Shortening and Ca2+ Transport in the Goto-Kakizaki Type 2 Diabetic Rat

2018 ◽  
pp. 57-68 ◽  
Author(s):  
K. A. SALEM ◽  
V. SYDORENKO ◽  
M. QURESHI ◽  
M. OZ ◽  
F. C. HOWARTH
Keyword(s):  
Ventricular Myocytes ◽  
Cellular Level ◽  
Diabetic Rat ◽  
Antidiabetic Agent ◽  
Inotropic Effects ◽  
And Control ◽  
Transmembrane Currents ◽  
Negative Inotropic Effects ◽  
Type 2 Diabetic

Pioglitazone (PIO) is a thiazolidindione antidiabetic agent which improves insulin sensitivity and reduces blood glucose in experimental animals and treated patients. At the cellular level the actions of PIO in diabetic heart are poorly understood. A previous study has demonstrated shortened action potential duration and inhibition of a variety of transmembrane currents including L-type Ca2+ current in normal canine ventricular myocytes. The effects of PIO on shortening and calcium transport in ventricular myocytes from the Goto-Kakizaki (GK) type 2 diabetic rat have been investigated. 10 min exposure to PIO (0.1-10 µM) reduced the amplitude of shortening to similar extents in ventricular myocytes from GK and control rats. 1 μM PIO reduced the amplitude of the Ca2+ transients to similar extents in ventricular myocytes from GK and control rats. Caffeine-induced Ca2+ release from the sarcoplasmic reticulum and recovery of Ca2+ transients following application of caffeine and myofilament sensitivity to Ca2+ were not significantly altered in ventricular myocytes from GK and control rats. Amplitude of L-type Ca2+ current was not significantly decreased in myocytes from GK compared to control rats and by PIO treatment. The negative inotropic effects of PIO may be attributed to a reduction in the amplitude of the Ca2+ transient however, the mechanisms remain to be resolved.

scholarly journals Perturbation of the mucosa-associated anaerobic gut microbiota in streptozotocin-induced diabetic rats

2021 ◽  
Vol 65 (1) ◽  
pp. 75-84
Author(s):  
Roland Wirth ◽  
Nikolett Bódi ◽  
Zita Szalai ◽  
Lalitha Chandrakumar ◽  
Gergely Maróti ◽  
...  
Keyword(s):  
Insulin Treatment ◽  
Relative Number ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Tissue Samples ◽  
Next Generation Dna Sequencing ◽  
Chronic Hyperglycaemia ◽  
And Control ◽  
Diabetic Rat Model ◽  
Anaerobic Environment

Our aim was to map the gut region-specific differences of the mucosa-associated microbiome distribution in a streptozotocin-induced diabetic rat model. Tissue samples from the duodenum, ileum and colon were collected 10 weeks after the onset of hyperglycaemia to analyse the mucosa-associated microbiota using next-generation DNA sequencing. Striking differences were observed in the mucosa-associated microbiota of the duodenum between diabetic and control rats. A significant invasion of the aerobic genus Mycoplasma was apparent in diabetes, and the abundance of the anaerobic phylum Firmicutes decreased massively. It is noteworthy that insulin treatment eliminated the Mycoplasma invasion in the duodenum and apparently restored the anaerobic environment in the mucosa. In the ileum the abundance of the phylum Firmicutes increased in the diabetic samples. Although the proportion of the phylum Proteobacteria decreased moderately, its composition changed significantly, and insulin treatment induced only minor alterations. In the diabetic samples of colon, the abundance of the phylum Firmicutes decreased slightly, the relative number of the bacteria in the phylum Bacteroidetes increased strongly as compared to the control values, and after insulin treatment this increase was more significant. Chronic hyperglycaemia has the most prominent effect on the mucosa-associated microbiota in the duodenum.

Metabolism of very-low-density lipoprotein and chylomicrons by streptozotocin-induced diabetic rat heart: effects of diabetes and lipoprotein preference

2008 ◽  
Vol 295 (5) ◽  
pp. E1106-E1116 ◽  
Author(s):  
You-Guo Niu ◽  
Rhys D. Evans
Keyword(s):  
Glucose Oxidation ◽  
Early Stage ◽  
Low Density Lipoprotein ◽  
Lipoprotein Metabolism ◽  
Density Lipoprotein ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
And Control

Very-low-density lipoprotein (VLDL) and chylomicrons (CM) are major sources of fatty acid supply to the heart, but little is known about their metabolism in diabetic myocardium. To investigate this, working hearts isolated from control rats and diabetic rats 2 wk following streptozotocin (STZ) injection were perfused with control and diabetic lipoproteins. Analysis of the diabetic lipoproteins showed that both VLDL and CM were altered compared with control lipoproteins; both were smaller and had different apolipoprotein composition. Heparin-releasable lipoprotein lipase (HR-LPL) activity was increased in STZ-induced diabetic hearts, but tissue residual LPL activity was decreased; moreover, diabetic lipoproteins stimulated HR-LPL activity in both diabetic and control hearts. Diabetic hearts oxidized lipoprotein-triacylglycerol (TAG) to a significantly greater extent than controls (>80% compared with deposition as tissue lipid), and the oxidation rate of exogenous lipoprotein-TAG was increased significantly in diabetic hearts regardless of TAG source. Significantly increased intracardiomyocyte TAG accumulation was found in diabetic hearts, although cardiac mechanical function was not inhibited, suggesting that lipotoxicity precedes impaired cardiac performance. Glucose oxidation was significantly decreased in diabetic hearts; additionally, however, diabetic lipoproteins decreased glucose oxidation in diabetic and control hearts. These results demonstrate increased TAG-rich lipoprotein metabolism concomitant with decreased glucose oxidation in type 1 diabetic hearts, and the alterations in cardiac lipoprotein metabolism may be due to the properties of diabetic TAG-rich lipoproteins as well as the diabetic state of the myocardium. These changes were not related to cardiomyopathy at this early stage of diabetes.

Sign in / Sign up

Export Citation Format

Share Document