scholarly journals Potassium current activated by depolarization of dissociated neurons from adult guinea pig hippocampus.

1988 ◽  
Vol 92 (2) ◽  
pp. 263-278 ◽  
Author(s):  
P Sah ◽  
A J Gibb ◽  
P W Gage
Keyword(s):  
Guinea Pig ◽  
Potassium Concentration ◽  
Type Equation ◽  
Potassium Currents ◽  
Equilibrium Potential ◽  
Extracellular Potassium ◽  
Extracellular Potassium Concentration ◽  
Ca1 Region ◽  
Average Maximum ◽  
Steady Level

Currents were generated by depolarizing pulses in voltage-clamped, dissociated neurons from the CA1 region of adult guinea pig hippocampus in solutions containing 1 microm tetrodotoxin. When the extracellular potassium concentration was 100 mM, the currents reversed at -8.1 +/- 1.6 mV (n = 5), close to the calculated potassium equilibrium potential of -7 mV. The currents were depressed by 30 mM tetraethylammonium in the extracellular solution but were unaffected by 4-aminopyridine at concentrations of 0.5 or 1 mM. It was concluded that the currents were depolarization-activated potassium currents. Instantaneous current-voltage curves were nonlinear but could be fitted by a Goldman-Hodgkin-Katz equation with PNa/PK = 0.04. Conductance-voltage curves could be described by a Boltzmann-type equation: the average maximum conductance was 65.2 +/- 15.7 nS (n = 9) and the potential at which gK was half-maximal was -4.8 +/- 3.9 mV (mean +/- 1 SEM, n = 10). The relationship between the null potential and the extracellular potassium concentration was nonlinear and could be fitted by a Goldman-Hodgkin-Katz equation with PNa/PK = 0.04. The rising phase of potassium currents and the decay of tail currents could be fitted with exponentials with single time constants that varied with membrane potential. Potassium currents inactivated to a steady level with a time constant of approximately 450 ms that did not vary with potential. The currents were depressed by substituting cobalt or cadmium for extracellular calcium but similar effects were not obtained by substituting magnesium for calcium.

Insulin stimulation of an electrogenic pump at high extracellular potassium concentration

1985 ◽  
Vol 249 (1) ◽  
pp. E12-E16
Author(s):  
F. S. Wu ◽  
K. Zierler
Keyword(s):  
Skeletal Muscle ◽  
Potassium Concentration ◽  
Equilibrium Potential ◽  
Extracellular Potassium ◽  
Insulin Stimulation ◽  
Rat Skeletal Muscle ◽  
Extracellular Potassium Concentration ◽  
High K ◽  
Na Ions ◽  
Stimulation Of

There is no agreement about the immediate mechanism by which insulin hyperpolarizes skeletal muscle, adipocytes, and myocardium. Of three candidates, one has been eliminated; the hyperpolarization is not secondary to an increase in intracellular [K]. There are reports that insulin hyperpolarizes by increasing relative permeability to K compared with that to Na ions, and other reports that insulin stimulates an ouabain-sensitive electrogenic Na-K exchange pump. Our evidence has been interpreted to support the former and deny the latter, when rat skeletal muscle is bathed at normal [K]. Crucial evidence for the latter has not been reported: insulin hyperpolarizes to a potential more negative than the K equilibrium potential. We now report that when rat caudofemoralis muscle is incubated with insulin at normal extracellular [K], then depolarized by increasing extracellular [K] to 38.4 mM, by equimolar substitution of KCl for NaCl, there is hyperpolarization compared with potentials of muscles treated similarly with respect to [K] but without insulin. Under these circumstances, the membrane potential in the presence of insulin is more negative than the new K equilibrium potential, and, in contrast to our previous experience with muscles bathed only in normal [K], the hyperpolarization in high [K] is reduced or eliminated by ouabain.

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.

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