Membrane Potentials in the Muscles of the South American Frog, Leptodactylus Ocelatus

1955 ◽  
Vol 32 (3) ◽  
pp. 539-546
Author(s):  
E. J. HARRIS ◽  
H. MARTINS-FERREIRA
Keyword(s):  
Ringer Solution ◽  
Resting Potential ◽  
Phosphate Solution ◽  
Constant Field ◽  
South American ◽  
The South ◽  
American Frog ◽  
K Concentration ◽  
Phosphate Solutions ◽  
External K

1. The resting potential of the fibres of the South American frog Leptodactylus ocelatus has been measured using microelectrodes. 2. In 2 mM. potassium Ringer solution values of 85-103 mV. were obtained. The value for a given muscle depends upon the external K concentration and the relation between resting potential and the concentrations of K, Na and Cl in the medium can be fitted to the constant field solution of the diffusion equation. 3. Use of phosphate solutions in place of chloride solutions led to lower resting potentials at a given K concentration, which is understandable since the contribution of Cl ions to the resting potential is not present in the phosphate solution. 4. The action potential was observed. Its rate of fall was less when the positive overshoot was low than when the overshoot was high. 5. Analyses of muscles and plasma were made.

scholarly journals Effect of acetylcholine on postjunctional membrane permeability in eel electroplaque.

1977 ◽  
Vol 70 (1) ◽  
pp. 23-36 ◽  
Author(s):  
N L Lassignal ◽  
A R Martin
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Membrane Permeability ◽  
Ionic Composition ◽  
Reversal Potential ◽  
Resting Potential ◽  
Constant Field ◽  
Free Solution ◽  
Positive Direction ◽  
External K

Acetylcholine (ACh) was applied iontophoretically to the innervated face of isolated eel electroplaques while the membrane potential was being recorded intracellularly. At the resting potential (about -85 mV) application of the drug produced depolarizations (ACh potentials) of 20 mV or more which became smaller when the membrane was depolarized and reversed in polarity at about zero membrane potential. The reversal potential shifted in the negative direction when external Na+ was partially replaced by glucosamine. Increasing external K+ caused a shift of reversal potential in the positive direction. It was concluded that ACh increased the permeability of the postjunctional membrane to both ions. Replacement of Cl- by propionate had no effect on the reversal potential. In Na+-free solution containing glucosamine the reversal potential was positive to the resting potential, suggesting that ACh increased the permeability to glucosamine. Addition of Ca++ resulted in a still more positive reversal potential, indicating an increased permeability to Ca++ as well. Analysis of the results indicated that the increases in permeability of the postjunctional membrane to K+, Na+, Ca++, and glucosamine were in the ratios of approximately 1.0:0.9:0.7:0.2, respectively. With these permeability ratios, all of the observed shifts in reversal potential with changes in external ionic composition were predicted accurately by the constant field equation.

The diffusion and electrogenic components of the membrane potential of hypoxic myocardium

1987 ◽  
Vol 65 (2) ◽  
pp. 246-251 ◽  
Author(s):  
Normand Leblanc ◽  
Elena Ruiz-Ceretti
Keyword(s):  
Membrane Potential ◽  
Sodium Pump ◽  
Resting Potential ◽  
Krebs Solution ◽  
Ventricular Muscle ◽  
Diffusion Component ◽  
K Concentration ◽  
Zero Potential ◽  
K Permeability ◽  
External K

The diffusion and electrogenic components of the resting potential of hypoxic ventricular muscle were separated by inhibition of the sodium pump with 10−4 M ouabain. The response to varying external K concentrations (Ko) was studied. Arteriaily perfused rabbit hearts were submitted to 60 min hypoxia in Krebs solution containing 5 mM K throughout or to different external K concentrations during the last 20 min of hypoxia. For K concentrations between 1.5 and 10 mM, hypoxia did not change the resting potential except for a slight hyperpolarization in 7.5 mM K. The diffusion component of the resting potential did not differ from the resting potential at Ko < 5 mM. An electrogenic potential of −3 to −6 mV was detectable at Ko values between 5 and 10 mM. The internal K concentration, Ki, was estimated from extrapolations to zero potential of the relation resting potential vs. Ko in normoxic and hypoxic hearts. These experiments revealed a decline of Ki of 16 mM with hypoxia. The variation of the diffusion potential with external K was fitted by a PNa:PK ratio five times lower than in normoxia. It has been concluded that an increase in K permeability and the persistence of electrogenic Na extrusion during hypoxia of rather short duration prevent membrane depolarization despite the myocardial K loss.

scholarly journals Cat Heart Muscle in Vitro

1962 ◽  
Vol 46 (2) ◽  
pp. 189-199 ◽  
Author(s):  
Ernest Page
Keyword(s):  
Steady State ◽  
Heart Muscle ◽  
Potential Difference ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Papillary Muscles ◽  
K Concentration ◽  
Cat Heart ◽  
External K

The steady state transmembrane resting potential difference (Vm) has been measured in quiescent papillary muscles. Vm was determined as a function of the external K concentration in Cl and SO4 solutions and compared with the K equilibrium potential. Other measurements were made after replacement of external Na by choline, K by Rb and Cs, and Cl by SO4, CH3SO4, and NO3. Effects on Vm of albumin, temperature, and variation in internal K concentration are described.

Purification and Properties of Laticeptin, an Antimicrobial Peptide from Skin Secretions of the South American Frog Leptodactylus laticeps

2006 ◽  
Vol 13 (4) ◽  
pp. 411-415 ◽  
Author(s):  
J. Conlon ◽  
Nadia Al-Ghaferi ◽  
Bency Abraham ◽  
Agnes Sonnevend ◽  
Jay King ◽  
...  
Keyword(s):  
Antimicrobial Peptide ◽  
South American ◽  
The South ◽  
Purification And Properties ◽  
Skin Secretions ◽  
American Frog

In vivo ionic exchange through the skin of the South American frog, Leptodactylus ocellatus

1968 ◽  
Vol 25 (1) ◽  
pp. 311-317 ◽  
Author(s):  
Alfredo Salibián ◽  
Silvia Pezzani-Hernández ◽  
Federico García Romeu
Keyword(s):  
South American ◽  
Ionic Exchange ◽  
The South ◽  
American Frog

scholarly journals A rapidly activating and slowly inactivating potassium channel cloned from human heart. Functional analysis after stable mammalian cell culture expression.

1993 ◽  
Vol 101 (4) ◽  
pp. 513-543 ◽  
Author(s):  
D J Snyders ◽  
M M Tamkun ◽  
P B Bennett
Keyword(s):  
Cell Lines ◽  
Time Course ◽  
Reversal Potential ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Constant Field ◽  
Slow Inactivation ◽  
Time Constants ◽  
K Concentration ◽  
External K

The electrophysiological properties of HK2 (Kv1.5), a K+ channel cloned from human ventricle, were investigated after stable expression in a mouse Ltk- cell line. Cell lines that expressed HK2 mRNA displayed a current with delayed rectifier properties at 23 degrees C, while sham transfected cell lines showed neither specific HK2 mRNA hybridization nor voltage-activated currents under whole cell conditions. The expression of the HK2 current has been stable for over two years. The dependence of the reversal potential of this current on the external K+ concentration (55 mV/decade) confirmed K+ selectivity, and the tail envelope test was satisfied, indicating expression of a single population of K+ channels. The activation time course was fast and sigmoidal (time constants declined from 10 ms to &lt; 2 ms between 0 and +60 mV). The midpoint and slope factor of the activation curve were Eh = -14 +/- 5 mV and k = 5.9 +/- 0.9 (n = 31), respectively. Slow partial inactivation was observed especially at large depolarizations (20 +/- 2% after 250 ms at +60 mV, n = 32), and was incomplete in 5 s (69 +/- 3%, n = 14). This slow inactivation appeared to be a genuine gating process and not due to K+ accumulation, because it was present regardless of the size of the current and was observed even with 140 mM external K+ concentration. Slow inactivation had a biexponential time course with largely voltage-independent time constants of approximately 240 and 2,700 ms between -10 and +60 mV. The voltage dependence of slow inactivation overlapped with that of activation: Eh = -25 +/- 4 mV and k = 3.7 +/- 0.7 (n = 14). The fully activated current-voltage relationship displayed outward rectification in 4 mM external K+ concentration, but was more linear at higher external K+ concentrations, changes that could be explained in part on the basis of constant field (Goldman-Hodgkin-Katz) rectification. Activation and inactivation kinetics displayed a marked temperature dependence, resulting in faster activation and enhanced inactivation at higher temperature. The current was sensitive to low concentrations of 4-aminopyridine, but relatively insensitive to external TEA and to high concentrations of dendrotoxin. The expressed current did not resemble either the rapid or the slow components of delayed rectification described in guinea pig myocytes. However, this channel has many similarities to the rapidly activating delayed rectifying currents described in adult rat atrial and neonatal canine epicardial myocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals The Origin of the Short-Circuit Current in the Isolated Skin of the South American Frog Leptodactylus ocellatus

1963 ◽  
Vol 47 (2) ◽  
pp. 393-402 ◽  
Author(s):  
José A. Zadunaisky ◽  
Oscar A. Candia ◽  
Dante J. Chiarandini
Keyword(s):  
Copper Ions ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Chloride Ions ◽  
Potential Difference ◽  
South American ◽  
The South ◽  
Net Flux ◽  
American Frog ◽  
Short Circuit Condition

In isolated skins of Leptodactylus ocellatus the short-circuit current is smaller than the sodium net flux and this difference disappears when the skins are bathed in solutions in which the chloride ions have been replaced by sulfate or methylsulfate ions. There is a net movement of chloride ions from outside to inside of the skins in the short-circuit condition with chloride Ringer's solutions bathing the skins. The addition of ouabain to the inside solution markedly reduced not only sodium net flux but also the chloride net influx found. Copper ions added to the outside solutions produced a rise in short-circuit current, as well as the known increase in potential difference. In sodium-free Ringer's (sodium replaced by choline) the orientation of the potential difference across the skins was reversed, the inside being negative instead of positive. The results are interpreted as direct or indirect indications of the presence of a net transfer of chloride ions from outside to inside of these frog skins.

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