scholarly journals Suppression of the hERG potassium channel response to premature stimulation by reduction in extracellular potassium concentration

2014 ◽  
Vol 2 (10) ◽  
pp. e12165 ◽  
Author(s):  
Dario Melgari ◽  
Chunyun Du ◽  
Aziza El Harchi ◽  
Yihong Zhang ◽  
Jules C. Hancox
Keyword(s):  
Potassium Channel ◽  
Potassium Concentration ◽  
Extracellular Potassium ◽  
Extracellular Potassium Concentration ◽  
Channel Response

The effect of ATP-sensitive potassium channel modulation on heart rate in isolated muskrat and guinea pig hearts.

1994 ◽  
Vol 197 (1) ◽  
pp. 101-118
Author(s):  
D R Streeby ◽  
T A McKean
Keyword(s):  
Heart Rate ◽  
Guinea Pig ◽  
Potassium Channel ◽  
Extracellular Potassium ◽  
Guinea Pig Heart ◽  
Channel Activation ◽  
Extracellular Potassium Concentration ◽  
Local Factors ◽  
Hypoxic Conditions ◽  
Vagal Innervation

Muskrats (Ondontra zibethicus) are common freshwater diving mammals exhibiting a bradycardia with both forced and voluntary diving. This bradycardia is mediated by vagal innervation; however, if hypoxia is present there may be local factors that also decrease heart rate. Some of these local factors may include ATP-sensitive potassium channel activation and extracellular accumulation of potassium ions, hydrogen ions and lactate. The purpose of this study was to investigate the role of these factors in the isolated perfused hearts of muskrats and of a non-diving mammal, the guinea pig. Although lactate and proton administration reduced heart rate in isolated muskrat and guinea pig hearts, there was no difference in the response to lactate and proton infusion between the two species. Muskrat hearts were more sensitive to the heart-rate-lowering effects of exogenously applied potassium than were guinea pig hearts. Early increases in extracellular potassium concentration during hypoxia are thought to be mediated by the ATP-sensitive potassium channel. Activation of these channels under normoxic conditions had a mildly negative chronotropic effect in both species; however, activation of these channels with Lemakalim under hypoxic conditions caused the guinea pig heart to respond with an augmented bradycardia similar to that seen in the hypoxic muskrat heart in the absence of drugs. Inhibition of these channels by glibenclamide during hypoxia was partially successful in blocking the bradycardia in guinea pig hearts, but inhibition of the same channels in hypoxic muskrat hearts had a damaging effect as two of five hearts went into contracture during the hypoxia. Thus, although ATP-sensitive potassium channels appear to have a major role in the bradycardia of hypoxia in guinea pigs, the failure to prevent the bradycardia by inhibition of these channels in muskrat hearts suggests that multiple factors are involved in the hypoxia-induced bradycardia in this species.

Disorders of potassium homeostasis

2010 ◽  
pp. 3831-3845 ◽  
Author(s):  
J Firth
Keyword(s):  
Membrane Potential ◽  
Potassium Concentration ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Normal Range ◽  
Critical Determinant ◽  
Potassium Homeostasis ◽  
Extracellular Potassium Concentration

The normal range of potassium concentration in serum is 3.5 to 5.0 mmol/litre and within cells it is 150 to 160 mmol/litre, the ratio of intracellular to extracellular potassium concentration being a critical determinant of cellular resting membrane potential and thereby of the function of excitable tissues....

Theoretical analysis of parameters leading to frequency modulation along an inhomogeneous axon

1976 ◽  
Vol 39 (4) ◽  
pp. 909-923 ◽  
Author(s):  
I. Parnas ◽  
S. Hochstein ◽  
H. Parnas
Keyword(s):  
Potassium Concentration ◽  
Single Step ◽  
Repetitive Firing ◽  
Extracellular Potassium ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Extracellular Potassium Concentration ◽  
Spike Shape ◽  
Single Spike ◽  
Low Pass

1. Theoretical computations were conducted on a computer model of a segmented, nonhomogeneous axon to understand the mechanism of frequency block of conduction. 2. The model is based on the Hodgkin-Huxley equations modified in several ways to better describe the cockroach axon. We used cockroach parameters where available. 3. The increase in fiber radius was spread over a series of segments to approximate a taper. We found that a taper allows a larger overall increase in fiber diameter than a single step to be successfully passed. 4. We studied effects on a train of impulses. The modified equations included effects due to changes in extracellular potassium concentration resulting from the repetitive firing of the axon. 5. An increase in diameter which allows a single spike to pass blocks the subsequent impulses in a train at the taper if potassium concentration variability is introduced. This could explain the low-pass filter characteristics of axon constrictions. 6. Results of the model fit well with the experiemental spike shape and height. Data were computed for the refractory period and its dependence on the taper parameters.

Sodium dependence of carnitine transport in isolated perfused adult rat hearts

1983 ◽  
Vol 244 (2) ◽  
pp. H247-H252 ◽  
Author(s):  
T. C. Vary ◽  
J. R. Neely
Keyword(s):  
Potassium Concentration ◽  
Sodium Concentration ◽  
Extracellular Potassium ◽  
Extracellular Potassium Concentration ◽  
Rat Hearts ◽  
Carrier Mediated Transport ◽  
Physiological Serum ◽  
Carnitine Transport ◽  
Extracellular Sodium ◽  
Carnitine Concentration

In heart muscle, the intracellular carnitine concentration is approximately 40 times higher than the plasma carnitine concentration, suggesting the existence of an active transport process. At physiological serum carnitine concentrations (44 microM), 80% of total myocardial carnitine uptake occurs via a carrier-mediated transport system. The mechanism of this carrier-mediated transport was studied in isolated perfused rat hearts. Carnitine transport showed an absolute dependence on the extracellular sodium concentration. The rate of carnitine transport was linearly related to the perfusate sodium concentration at every perfusate carnitine concentration examined (15-100 microM). Total removal of extracellular sodium completely abolished the carrier-mediated transport. Decreasing the perfusate potassium concentration from a control of 5.9 to 0.6 mM stimulated transport by 35%, whereas increasing the extracellular potassium concentration from 5.9 to 25 mM reduced transport by 60%. The carrier-mediated transport was inversely proportional to the extracellular potassium concentration. Acetylcholine (10(-3) M), isoproterenol (10(-7) M), or ouabain (10(-3) did not alter the rate of carnitine transport. Addition of tetrodotoxin (10(-5) stimulated carnitine transport by about 40%, while gramicidin S (5 X 10(-6) M) decreased uptake by about 18% relative to control. The data provide evidence that carnitine transport by cardiac cells occurs by a Na+-dependent cotransport mechanism that is dependent on the Na+ electrochemical gradient.

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