Resting membrane potentials: a student test of alternate hypotheses.

The frog sartorius muscle is a model tissue for demonstrating to physiology students the principles underlying both membrane phenomena and hypothesis testing. Myocytes can be impaled with conventional glass microelectrodes to measure membrane voltage (Vm). Further, Vm is observed as extracellular K+ is altered and a K+ channel blocker is added. After the experiment, students examine the underlying assumptions of the Nernst equilibrium and the Goldman-Hodgkin-Katz equation. They ultimately determine which of the two algorithms best predicts the measured Vm. In addition, students learn micromanipulation and impalement techniques. This experiment facilitates the student's understanding of membrane permeability, ionic gradients, and membrane voltage.

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Primary involvement of K+ conductance in membrane resonance of trigeminal root ganglion neurons

Journal of Neurophysiology ◽

10.1152/jn.1988.59.1.77 ◽

1988 ◽

Vol 59 (1) ◽

pp. 77-89 ◽

Cited By ~ 29

Author(s):

E. Puil ◽

B. Gimbarzevsky ◽

I. Spigelman

Keyword(s):

Electrical Properties ◽

Channel Blocker ◽

Complex Impedance ◽

Membrane Potentials ◽

K Channel ◽

Bathing Medium ◽

Trigeminal Root ◽

Membrane Resonance ◽

Ganglion Neurons ◽

Impedance Magnitude

1. The complex impedances and impedance magnitude functions were obtained from neurons in in vitro slices of trigeminal root ganglia using frequency-domain analyses of intracellularly recorded voltage responses to specified oscillatory input currents. A neuronal model derived from linearized Hodgkin-Huxley-like equations was used to fit the complex impedance data. This procedure yielded estimates for membrane electrical properties. 2. Membrane resonance was observed in the impedance magnitude functions of all investigated neurons at their initial resting membrane potentials and was similar to that reported previously for trigeminal root ganglion neurons in vivo. Tetrodotoxin (10(-6) M), a Na+-channel blocker, applied in the bathing medium for 20 min produced only minor changes, if any, in the resonance, although gross impairment of Na+-spike electrogenesis was apparent in most of the neurons. Brief applications (1-5 min) of a K+-channel blocker, tetraethylammonium (TEA; 10(-2) M), increased the impedance magnitude and abolished, in a reversible manner, the resonant behavior. In all cases, the resonant frequency was decreased by TEA administration prior to total blockade of resonance. 3. The TEA-induced blockade of resonance was associated with decreases in the estimates of the membrane conductances, without significant alterations of input capacitance. A particularly large decrease was observed in Gr, the time-invariant resting conductance that includes a lumped leak conductance component. The voltage- and time-dependent conductance, GL, and associated relaxation time constant, tau u, also declined progressively during administration of TEA. 4. Systematic variations in the membrane potentials of trigeminal root ganglion neurons were produced by intracellular injections of long-lasting step currents with superposition of the oscillatory current stimuli, in order to assess the effects of TEA on the relationship of the electrical properties to the membrane potential. Applications of TEA led to a depolarizing shift in the dependence of the membrane property estimates, suggesting voltage-dependence of the effects of TEA on presumed K+ channels in the membrane. 5. These data suggest a primary involvement of K+ conductance in the genesis of membrane resonance. This electrical behavior or its ionic mechanism is a major modulator of the subthreshold electrical responsiveness of trigeminal root ganglion neurons.

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Changes in the Membrane Permeability of Frog's Sartorius Muscle Fibers in Ca-Free EDTA Solution

The Journal of General Physiology ◽

10.1085/jgp.47.2.379 ◽

1963 ◽

Vol 47 (2) ◽

pp. 379-392 ◽

Cited By ~ 25

Author(s):

H. Kimizuka ◽

K. Koketsu

Keyword(s):

Membrane Permeability ◽

Chloride Content ◽

Chloride Ions ◽

Sartorius Muscle ◽

Constant Field ◽

Sodium Influx ◽

Sodium Potassium ◽

Edta Solution ◽

Frog Sartorius ◽

Sodium And Potassium

The changes in the membrane permeability to sodium, potassium, and chloride ions as well as the changes in the intracellular concentration of these ions were studied on frog sartorius muscles in Ca-free EDTA solution. It was found that the rate constants for potassium and chloride efflux became almost constant within 10 minutes in the absence of external calcium ions, that for potassium increasing to 1.5 to 2 times normal and that for chloride decreasing about one-half. The sodium influx in Ca-free EDTA solution, between 30 and 40 minutes, was about 4 times that in Ringer's solution. The intracellular sodium and potassium contents did not change appreciably but the intracellular chloride content had increased to about 4 times normal after 40 minutes. By applying the constant field theory to these results, it was concluded that (a) PCl did not change appreciably whereas PK decreased to a level that, in the interval between 10 and 40 minutes, was about one-half normal, (b) PNa increased until between 30 and 40 minutes it was about 8 times normal. The low value of the membrane potential between 30 and 40 minutes was explained in terms of the changes in the membrane permeability and the intracellular ion concentrations. The mechanism for membrane depolarization in this solution was briefly discussed.

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Changes in membrane potentials, K content, and fiber structure in irradiated frog sartorius muscle

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1960.198.4.709 ◽

1960 ◽

Vol 198 (4) ◽

pp. 709-714 ◽

Cited By ~ 16

Author(s):

Edgar B. Darden

Keyword(s):

Membrane Potential ◽

Membrane Potentials ◽

Sartorius Muscle ◽

Fiber Structure ◽

Ringer’S Solution ◽

Intact Muscle ◽

Radiation Induced ◽

Induced Changes ◽

Histologic Changes ◽

Frog Sartorius

Changes in membrane potential, K content, and fiber structure were studied in excised frog sartorius muscles that had received massive single doses (50–200 kr) of ionizing radiation. With muscle in normal Ringer's solution at 25°C, the median membrane potential declined and K leakage increased progressively, as measured at intervals, after exposure doses above ∼100 kr; in K-rich Ringer's solution, decline was appreciably slower. In individual irradiated fibers, membrane potentials recorded at different points along a fiber tended to be nonuniform. When subsequent histologic alteration occurred, it often originated as a focal disorganization of structure in a region of minimum membrane potential. Visible pathologic changes resembled in part Zenker degeneration in intact muscle. It is suggested that decline in membrane potential, histologic changes, and increased K leakage are different expressions of the same basic radiation lesion. Radiation-induced changes were markedly retarded by posttreatment storage at 3°C.

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The effects of modified ringer's solutions on the membrane potentials of innervated and denervated frog sartorius muscle fibers

Journal of Cellular Physiology ◽

10.1002/jcp.1040670113 ◽

1966 ◽

Vol 67 (1) ◽

pp. 107-123 ◽

Cited By ~ 2

Author(s):

Leonard Levine

Keyword(s):

Muscle Fibers ◽

Membrane Potentials ◽

Sartorius Muscle ◽

Frog Sartorius Muscle ◽

Frog Sartorius

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RECOVERY CURVES OF THRESHOLDS OF MUSCLE SPINDLE, LEAF-LIKE AND TENDON RECEPTORS IN THE FROG SARTORIUS MUSCLE AFTER AN ANTIDROMIC DISCHARGE

The Japanese Journal of Physiology ◽

10.2170/jjphysiol.18.731 ◽

1968 ◽

Vol 18 (6) ◽

pp. 731-745 ◽

Cited By ~ 8

Author(s):

Fumio ITO

Keyword(s):

Muscle Spindle ◽

Sartorius Muscle ◽

Recovery Curves ◽

Frog Sartorius Muscle ◽

Frog Sartorius

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Prepotentials and unidirectional propagation in myocardium

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1961.201.5.873 ◽

1961 ◽

Vol 201 (5) ◽

pp. 873-880 ◽

Cited By ~ 14

Author(s):

T. Hoshiko ◽

Nick Sperelakis

Keyword(s):

Current Flow ◽

Reverse Direction ◽

Sartorius Muscle ◽

Potential Response ◽

Ringer’S Solution ◽

Current Pulses ◽

Negative Current ◽

Reversed Polarity ◽

Bidirectional Propagation ◽

Frog Sartorius

In frog ventricular strips bathed in Ca-free Ringer's solution containing 6–30 mm/liter Mg and treated with conditioning current pulses, propagation became impaired. An exaggerated foot, or prepotential, was consistently more prominent when the conditioned strip was stimulated from one end than from the other. Occasionally a prepotential in isolation alternated with a prepotential plus action potential response. After further treatment with current pulses, propagation failed in the direction of negative current flow. Thresholds of impaled cells were identical. Bidirectional propagation was restored in Ringer's solution. Conditioning pulses of reversed polarity induced unidirectional propagation in the reverse direction. Propagation in frog sartorius muscle was not blocked under similar conditions. Prepotentials and unidirectional propagation may be explained by junctional transmission from cell to cell.

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Arabidopsis AtCNGC10 rescues potassium channel mutants of E. coli, yeast and Arabidopsis and is regulated by calcium/calmodulin and cyclic GMP in E. coli

Functional Plant Biology ◽

10.1071/fp04233 ◽

2005 ◽

Vol 32 (7) ◽

pp. 643 ◽

Cited By ~ 51

Author(s):

Xinli Li ◽

Tamás Borsics ◽

H. Michael Harrington ◽

David A. Christopher

Keyword(s):

Channel Blocker ◽

K Channel ◽

Structure Characteristic ◽

Dependent Manner ◽

Wild Type ◽

Yeast Saccharomyces Cerevisiae ◽

E Coli ◽

Diverse Species ◽

The Family ◽

Low K

We have isolated and characterised AtCNGC10, one of the 20 members of the family of cyclic nucleotide (CN)-gated and calmodulin (CaM)-regulated channels (CNGCs) from Arabidopsis thaliana (L.) Heynh. AtCNGC10 bound CaM in a C-terminal subregion that contains a basic amphiphillic structure characteristic of CaM-binding proteins and that also overlaps with the predicted CN-binding domain. AtCNGC10 is insensitive to the broad-range K+ channel blocker, tetraethylammonium, and lacks a typical K+-signature motif. However, AtCNGC10 complemented K+ channel uptake mutants of Escherichia coli (LB650), yeast (Saccharomyces cerevisiae CY162) and Arabidopsis (akt1-1). Sense 35S-AtCNGC10 transformed into the Arabidopsis akt1-1 mutant, grew 1.7-fold better on K+-limited medium relative to the vector control. Coexpression of CaM and AtCNGC10 in E. coli showed that Ca2+ / CaM inhibited cell growth by 40%, while cGMP reversed the inhibition by Ca2+ / CaM, in a AtCNGC10-dependent manner. AtCNGC10 did not confer tolerance to Cs+ in E. coli, however, it confers tolerance to toxic levels of Na+ and Cs+ in the yeast K+ uptake mutant grown on low K+ medium. Antisense AtCNGC10 plants had 50% less potassium than wild type Columbia. Taken together, the studies from three evolutionarily diverse species demonstrated a role for the CaM-binding channel, AtCNGC10, in mediating the uptake of K+ in plants.

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Enhanced role of K+ channels in relaxations of hypercholesterolemic rabbit carotid artery to NO

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1995.269.3.h805 ◽

1995 ◽

Vol 269 (3) ◽

pp. H805-H811 ◽

Cited By ~ 16

Author(s):

S. Najibi ◽

R. A. Cohen

Keyword(s):

Carotid Artery ◽

Sodium Nitroprusside ◽

Channel Blocker ◽

Isometric Tension ◽

K Channel ◽

K Channels ◽

Rabbit Carotid Artery ◽

Cyclic Monophosphate ◽

Endothelium Dependent Relaxation

Endothelium-dependent relaxations to acetylcholine remain normal in the carotid artery of hypercholesterolemic rabbits, but unlike endothelium-dependent relaxations of normal rabbits, they are inhibited by charybdotoxin, a specific blocker of Ca(2+)-dependent K+ channels. Because nitric oxide (NO) is the mediator of endothelium-dependent relaxation and can activate Ca(2+)-dependent K+ channels directly or via guanosine 3',5'-cyclic monophosphate, the present study investigated the role of Ca(2+)-dependent K+ channels in relaxations caused by NO, sodium nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Brc-GMP) in hypercholesterolemic rabbit carotid artery. Isometric tension was measured in rabbit carotid artery denuded of endothelium from normal and hypercholesterolemic rabbits which were fed 0.5% cholesterol for 12 wk. Under control conditions, relaxations to all agents were similar in normal and hypercholesterolemic rabbit arteries. Charybdotoxin had no significant effect on relaxations of normal arteries to NO, sodium nitroprusside, or 8-BrcGMP, but the Ca(2+)-dependent K+ channel blocker significantly inhibited the relaxations caused by each of these agents in the arteries from hypercholesterolemic rabbits. By contrast, relaxations to the calcium channel blocker nifedipine were potentiated to a similar extent by charybdotoxin in both groups. In addition, arteries from hypercholesterolemic rabbits relaxed less than normal to sodium nitroprusside when contracted with depolarizing potassium solution. These results indicate that although nitrovasodilator relaxations are normal in the hypercholesterolemic rabbit carotid artery, they are mediated differently, and to a greater extent, by Ca(2+)-dependent K+ channels. These data also suggest that K+ channel-independent mechanism(s) are impaired in hypercholesterolemia.

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