Potassium loss from hypoxic myocardium: influence of external K concentration

1987 ◽  
Vol 65 (5) ◽  
pp. 861-866 ◽  
Author(s):  
Normand Leblanc ◽  
Elena Ruiz-Ceretti ◽  
Denis Chartier
Keyword(s):  
Electrical Activity ◽  
Sodium Content ◽  
Total Water ◽  
Tissue Samples ◽  
Normal Medium ◽  
High K ◽  
Voltage Dependent ◽  
External Potassium ◽  
K Concentration ◽  
External K

The influence of external potassium Ko and tetraethylammonium on the cellular K content of hypoxic myocardium was investigated. Perfused rabbit hearts were submitted to 60 min hypoxia in medium containing 5 mM K throughout or either low (1.5 mM) or high (10 mM) K during the last 20 min of hypoxia. Paced electrical activity (2.5 Hz) was kept throughout the experiments. Tissue samples excised from the left ventricle were analyzed for total water, inulin space, and Na and K content. Lowering Ko to 1.5 mM increased both K loss and Na accumulation. Addition of 3.5 mM RbCl under these conditions reversed Na accumulation to levels found for hypoxia in normal medium but did not modify the cellular K loss. Tetraethylammonium (10 mM) did not alter Na accumulation but partly prevented the decrease in K content produced by hypoxia. A similar effect was observed by increasing Ko to 10 mM. At this high Ko prolongation of hypoxia did not enhance K loss. Abolition of electrical activity by TTX in a high K solution prevented K loss and reduced the sodium content. These results are consistent with the view that voltage-dependent channels are implicated in the K loss induced by hypoxia or ischemia. Furthermore, they indicate that the K loss may be modulated by external K because of the influence of the electrochemical gradient on passive K efflux and thus provide an explanation for the existence of a plateau in the early extracellular K accumulation observed during cardiac ischemia.

Dependence of tonic tension on extracellular calcium in rat extraocular muscle

1987 ◽  
Vol 253 (3) ◽  
pp. C375-C383 ◽  
Author(s):  
D. J. Chiarandini ◽  
J. Jacoby
Keyword(s):  
Extraocular Muscle ◽  
Specific Interactions ◽  
Contraction Coupling ◽  
Resting Tension ◽  
High K ◽  
Voltage Dependent ◽  
K Concentration ◽  
The Right ◽  
Tonic Tension ◽  
Ca2 Channels

Ca2+-free saline containing 3.0 mM Mg2+ virtually abolishes the tonic tension evoked by depolarization with a high K+ concentration of the tonic multiply innervated fibers of rat extraocular muscles. The tonic tension abolished by Ca2+ withdrawal is restored when Ca2+ is substituted by Sr2+ but not by Ni2+. The increase of Mg2+ reduces the tonic tension and displaces the tension-log K+ relationship to the right. Cd2+ significantly reduces the tension amplitude but does not shift the tension-log K+ relationship. The organic blocker of Ca2+ channels, nifedipine (1-10 microM), has no effect on the tonic tension. In contrast, diltiazem (20 microM) reduces the amplitude of the responses without changing the tension-log K+ relationship. Both foreign anions NO3- and SCN- potentiate tonic tension without changing the tension-log K+ relationship. SCN- increases the resting tension of the muscle; this effect depends on Ca2+. In conclusion, the disappearance of tonic tension after Ca2+ withdrawal is not due to depolarization of the fibers or inactivation of the contractile responses. It is suggested that entry of extracellular Ca2+, via a voltage-dependent Ca2+ conductance, or specific interactions of Ca2+ with membrane sites involved in the regulation of excitation-contraction coupling play a role in evoking tension in tonic fibers.

Depolarization reverses age-related decrease of spontaneous transmitter release

1991 ◽  
Vol 70 (5) ◽  
pp. 2066-2071 ◽  
Author(s):  
W. B. Alshuaib ◽  
M. A. Fahim
Keyword(s):  
Nerve Terminal ◽  
Transmitter Release ◽  
Nerve Terminals ◽  
Tetraacetic Acid ◽  
Ca Channels ◽  
Age Related ◽  
High K ◽  
Voltage Dependent ◽  
K Concentration ◽  
Period Of Oscillation

The effect of increasing extracellular Ca concentration on spontaneous transmitter release was studied at soleus nerve terminals of young (10 mo) and old (24 mo) C57BL/6J mice depolarized by high extracellular K concentration ([K]o). By using intracellular recording, miniature end-plate potentials (MEPPs) were first recorded in a normal [K]o Krebs solution. Subsequently, MEPPs were recorded in high [K]o Krebs solutions with four different Ca concentrations: Ca-free/ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and 0.5, 1.5, and 2.5 mM Ca. In both the normal [K]o Krebs and the Ca-free-high [K]o Krebs solutions, MEPP frequency was lower at old than at young nerve terminals. In the three high [K]o Krebs solutions with Ca, MEPP frequency was progressively higher at old than at young nerve terminals with higher Ca concentrations. Periodic oscillations were observed in MEPP frequency of depolarized nerve terminals. The period of oscillation was inversely proportional to spontaneous transmitter release. These results demonstrate that when the nerve terminal is depolarized, permeability of the terminal membrane to Ca increases because of opening of voltage-dependent Ca channels. In the present study resting MEPP frequency was lower at old than at young terminals. On depolarization, MEPP frequency became higher at old than at young terminals. The study demonstrates that voltage-dependent Ca entry increases during aging at the soleus nerve terminal.

Changes in the intracellular free calcium concentration of Aplysia and leech neurones measured with calcium-sensitive microelectrodes

1987 ◽  
Vol 65 (5) ◽  
pp. 934-939 ◽  
Author(s):  
Joachim W. Deitmer ◽  
Roger Eckert ◽  
Wolf-R. Schlue
Keyword(s):  
Calcium Concentration ◽  
Neuronal Membrane ◽  
Free Calcium ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
K Current ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration ◽  
K Concentration ◽  
External K

The intracellular free Ca concentration was measured in invertebrate neurones using single-barrelled and double-barrelled neutral-carrier microelectrodes. The electrodes were calibrated in solutions containing different Ca concentrations between 1 mM and 0.01 μM. The electrode responses were also tested at different ionic strengths and at varying Na concentrations. The electrodes responded with 25–30 mV per 10-fold change in Ca concentration between 1 mM and 1 μM and with 10–25 mV between 1 and 0.1 μM Ca. The intracellular free Ca concentration was measured to be between 0.1 and 0.7 μM in the neurones. The changes of intracellular Ca in identified voltage-clamped neurones of Aplysia californica were recorded during iontophoretic injections of Ca2+ or EGTA. The decrease of intracellular Ca following EGTA injection was correlated with the suppression of the Ca-dependent K current and with the reduction of Ca-induced inactivation of voltage-dependent Ca current. In identified neurones of the leech Hirudo medicinalis a reversible increase of intracellular Ca2+ was recorded after inhibition of the Na–K pump, either by addition of ouabain (0.5 mM) or by lowering the external K concentration (0.2 mM). This rise in intracellular Ca2+ did not occur, and was even reversed, in the absence of external Na, suggesting the existence of Na–Ca exchange across the leech neuronal membrane.

scholarly journals Energetics of Shaker K channels block by inactivation peptides.

1993 ◽  
Vol 102 (6) ◽  
pp. 977-1003 ◽  
Author(s):  
R D Murrell-Lagnado ◽  
R W Aldrich
Keyword(s):  
Ionic Strength ◽  
Electrostatic Interactions ◽  
Time Course ◽  
Free Peptide ◽  
Terminal Domain ◽  
Voltage Dependent ◽  
Inactivation Process ◽  
K Concentration ◽  
Association Rate Constants ◽  
External K

A synthetic peptide of the NH2-terminal inactivation domain of the ShB channel blocks Shaker channels which have an NH2-terminal deletion and mimics many of the characteristics of the intramolecular inactivation reaction. To investigate the role of electrostatic interactions in both peptide block and the inactivation process we measured the kinetics of block of macroscopic currents recorded from the intact ShB channel, and from ShB delta 6-46 channels in the presence of peptides, at different ionic strengths. The rate of inactivation and the association rate constants (k(on)) for the ShB peptides decreased with increasing ionic strength. k(on) for a more positively charged peptide was more steeply dependent on ionic strength consistent with a simple electrostatic mechanism of enhanced diffusion. This suggests that a rate limiting step in the inactivation process is the diffusion of the NH2-terminal domain towards the pore. The dissociation rates (k(off)) were insensitive to ionic strength. The temperature dependence of k(on) for the ShB peptide was very high, (Q10 = 5.0 +/- 0.58), whereas k(off) was relatively temperature insensitive (Q10 approximately 1.1). The results suggest that at higher temperatures the proportion of time either the peptide or channel spends in the correct conformation for binding is increased. There were two components to the time course of recovery from block by the ShB peptide, indicating two distinct blocked states, one of which has similar kinetics and dependence on external K+ concentration as the inactivated state of ShB. The other is voltage-dependent and at -120 mV is very unstable. Increasing the net charge on the peptide did not increase sensitivity to knock-off by external K+. We propose that the free peptide, having fewer constraints than the tethered NH2-terminal domain binds to a similar site on the channel in at least two different conformations.

Nombres de Transport, tK, tNa et tca Pour la Membrane de la Cellule Hépatique In Vivo

1972 ◽  
Vol 50 (5) ◽  
pp. 416-422 ◽  
Author(s):  
Jean Pierre Caillé ◽  
O. F. Schanne
Keyword(s):  
Membrane Potential ◽  
Liver Cell ◽  
Ionic Mobility ◽  
Irreversible Thermodynamics ◽  
Transport Numbers ◽  
Experimental Conditions ◽  
External Potassium ◽  
K Concentration ◽  
External K

We measured the membrane potential of the liver cell in vivo at 38 °C as we increased the external potassium. For the range of K concentration from 20.4 to 78 mM, the membrane potential of the liver cell decreased with a slope of 20.2 mV per decade change in external K concentration. The tissue content of K, Na, and Cl was analyzed under the same experimental conditions. The cytoplasmic resistivity (111 ± 17.5 Ω-cm) was used as a criterion for the state of the ions in the cytoplasm. This result, when it is compared with the value predicted from the ionic content, suggests that either the ionic mobility or the ionic activity in the cytoplasm of the liver cell is less than in a simple salt solution. An analytical expression, derived with the use of irreversible thermodynamics, permits us to calculate the transport numbers for the ions K, Na, and Cl in the membrane of the liver cell (tK 0.28, tNa 0.12, tCl 0.61).

scholarly journals Cat Heart Muscle in Vitro

1960 ◽  
Vol 44 (2) ◽  
pp. 327-344 ◽  
Author(s):  
Ernest Page ◽  
A. K. Solomon
Keyword(s):  
Papillary Muscles ◽  
Total Water ◽  
Inulin Space ◽  
Wet Weight ◽  
K Concentration ◽  
Cell Volumes ◽  
Cat Heart ◽  
External K

Methods have been developed for the simultaneous determination of total water, inulin space, and K and Na content in muscles of 0.5 to 10 mg. wet weight. These methods have been used to define steady state conditions with respect to intracellular K concentration in papillary muscles from cat hearts perfused and contracting isometrically at 27–28°C. and at 37–38°C. Cell volumes and intracellular ionic concentrations have been followed as a function of the external K concentration and compared with values predicted on the basis of electroneutrality and osmotic equilibrium.

scholarly journals Changes of total water and sucrose space accompanying induced ion uptake or phosphate swelling of rat liver mitochondria

1968 ◽  
Vol 106 (3) ◽  
pp. 759-766 ◽  
Author(s):  
E J Harris ◽  
K. Van Dam
Keyword(s):  
Rat Liver ◽  
Tritiated Water ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Scattering Method ◽  
Total Water ◽  
Cation Uptake ◽  
High K ◽  
K Concentration ◽  
Phosphate Addition

1. Total water exchangeable with tritiated water and sucrose space were measured in rat liver mitochondria during the uptake of K+ induced by valinomycin and the release caused by nigericin. The K+ content and the sucrose-inaccessible water rose and fell together. 2. Swelling resulting from phosphate addition in a medium of high K+ concentration was associated mainly with increased sucrose-accessible water, which carried dissolved K+. This change was reversed by addition of ATP. 3. The response of the sucrose-inaccessible space to changed osmolarity was qualitatively that expected if the mitochondrial K+ is assumed to be present in this space with a univalent anion. 4. It is brought out that the light-scattering method fails to distinguish between changes in sucrose space and in sucrose-inaccessible space, which in the present experiments could be altered respectively by phosphate (in high K+ solution) and by cation uptake induced by antibiotic.

Ionic mechanisms underlying electrical slow waves in canine airway smooth muscle

1998 ◽  
Vol 275 (3) ◽  
pp. L516-L523 ◽  
Author(s):  
Luke J. Janssen ◽  
Chris Hague ◽  
Roopung Nana
Keyword(s):  
Smooth Muscle ◽  
Channel Blocker ◽  
Niflumic Acid ◽  
Slow Waves ◽  
Bronchial Smooth Muscle ◽  
High K ◽  
Voltage Dependent ◽  
Ionic Mechanisms ◽  
Opening And Closing ◽  
External K

In canine bronchial smooth muscle (BSM), spasmogens evoke oscillations in membrane potential (“slow waves”). The depolarizing phase of the slow waves is mediated by voltage-dependent Ca2+ channels; we examined the roles played by Cl− and K+ currents and Na+-K+-ATPase activity in mediating the repolarizing phase. Slow waves were evoked using tetraethylammonium (25 mM) in the presence or absence of niflumic acid (100 μM; Cl− channel blocker) or ouabain (10 μM; block Na+-K+-ATPase) or after elevating external K+concentration ([K+]) to 36 mM (to block K+ currents); curve fitting was performed to quantitate the rates of rise/fall and frequency under these conditions. Slow waves were markedly slowed, and eventually abolished, by niflumic acid but were unaffected by ouabain or high [K+]. Electrically evoked slow waves were also blocked in similar fashion by niflumic acid. We conclude that the repolarization phase is mediated by Ca2+-dependent Cl− currents. This information, together with our earlier finding that the depolarizing phase is due to voltage-dependent Ca2+ current, suggests that slow waves in canine BSM involve alternating opening and closing of Ca2+ and Cl− channels.

Accumulation of inactivation in a cloned transient K+ channel (AKv1.1a) of Aplysia

1995 ◽  
Vol 74 (3) ◽  
pp. 1248-1257 ◽  
Author(s):  
Y. Furukawa
Keyword(s):  
Short Interval ◽  
Low Frequency ◽  
K Channel ◽  
Amino Terminal ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Inactivation Gating ◽  
A Cell ◽  
K Concentration ◽  
External K

1. Inactivation of a cloned Aplysia K+ channel, AKv1.1a, expressed in Xenopus oocytes was examined by a cell-attached macropatch recording. A fast macroscopic inactivation (the time constant for decay was in the range of 20-40 ms) in response to a depolarizing command pulse was insensitive to the concentration of external K+ (2-100 mM KCl). 2. By contrast, recovery from inactivation was extremely slow and dependent on external K+. When the concentration of external KCl was 2-3 mM, a patched membrane had to be held at hyperpolarized potential for > 40 s for a full recovery. The recovery was greatly accelerated if external K+ concentration was increased. A tail current following a command pulse long enough to inactivate most of the channels showed a marked rising phase. 3. A consequence of the slow recovery from inactivation was that AKv1.1a showed a marked accumulation of the inactivation following repetitive pulses, even at low frequency (< 0.1 Hz). When two depolarizing pulses were applied at a short interval, the current during a second pulse was smaller than the current at the end of the preceding pulse. This is a phenomenon called "cumulative inactivation." The onset and the extent of cumulative inactivation of AKv1.1a were voltage dependent but relatively insensitive to external K+ concentration. An amino terminal deletion mutant of AKv1.1a that lacks the fast N-type inactivation did not show cumulative inactivation. 4. These results suggest that the inactivation gating by the amino terminal region of AKv1.1a has a similarity to open-channel blockade, and that the cumulative inactivation can also be dependent on the amino terminal cytoplasmic domain of K+ channels.

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