Unidirectional flux ratio for potassium ions in depolarized frog skeletal muscle

1981 ◽  
Vol 241 (1) ◽  
pp. C68-C75 ◽  
Author(s):  
B. C. Spalding ◽  
O. Senyk ◽  
J. G. Swift ◽  
P. Horowicz
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Flux Ratio ◽  
External Solution ◽  
Resting Potential ◽  
Frog Skeletal Muscle ◽  
High K ◽  
Sigmoidal Curve ◽  
K Concentration ◽  
Low K

Small bundles of frog skeletal muscle fibers were loaded with 305 mM K+ and 120 mM Cl-, and 42K+ tracer efflux and influx were measured as a function of external K+ concentration ([K+]o) at a resting potential of -2 mV. As [K+]o was lowered from 305 mM, efflux decreased along a markedly sigmoidal curve, reaching a constant nonzero value at low [K+]o. Influx varied linearly with [K+]o at low [K+]o and more steeply at higher [K+]o. The ratio of influx to efflux was described by the equation: influx/efflux = exp[-n(V - VK)F/RT] with n = 2 at high [K+]o, but the ratio approached this equation with n = 1 at low [K+]o. Efflux did not depend on [K+]o when the membrane potential was raised to +36 mV, whereas at low [K+]o decreasing the membrane potential to -19 mV further activated the efflux. The results are discussed in terms of an inwardly rectifying potassium channel with two or more activating sites within the membrane that bind K+ and are accessible from the external solution.

Repolarization-Induced Reactivation of Contracture Tension in Frog Skeletal Muscle

1973 ◽  
Vol 51 (5) ◽  
pp. 324-334 ◽  
Author(s):  
J. G. Foulks ◽  
J. A. D. Miller ◽  
Florence A. Perry
Keyword(s):  
Skeletal Muscle ◽  
Relaxation Rate ◽  
Frog Skeletal Muscle ◽  
Maximum Tension ◽  
Long Duration ◽  
High K ◽  
Regulation Of Contraction ◽  
Low K ◽  
Dependent Processes

In solutions containing perchlorate in place of chloride frog toe muscles or small bundles of semitendinosus fibers undergo maximum potassium (K) contractures of long duration at low [K]0 (5–10 mM). After relaxation at high [K]0, large protracted "reactivation" contractures (70–90% of maximum tension) again develop when repolarization is accomplished by a reduction of [K]0 to 2.5–10 mM. Somewhat smaller contractures also appear during repolarization at lower perchlorate concentrations (8–12 mM). The effects of perchlorate include disproportionate shifts in the relation between log [K]0 and K-contracture tension, and between log [K]0 and relaxation rate. Similar but smaller effects are observed in the presence of 1 mM caffeine or 1.5 mM chloroform. These observations implicate at least two potential-dependent processes in the regulation of contraction in frog twitch muscle.

scholarly journals The Membrane Potential of Acetabularia mediterranea

1970 ◽  
Vol 55 (6) ◽  
pp. 802-821 ◽  
Author(s):  
H. D. W. Saddler
Keyword(s):  
Membrane Potential ◽  
Low Temperature ◽  
Kinetic Data ◽  
External Solution ◽  
High K ◽  
Nonsteady State ◽  
Tracer Kinetic ◽  
Acetabularia Mediterranea ◽  
Low K

The cytoplasm of an Acetabularia cell is normally at a potential of about -170 mv relative to the external solution; the vacuole is also at this potential. Although there is strict flux equilibrium for all ions, the potential is more negative than the Nernst potentials of any of the permeating ions. Darkness, CCCP, low temperature, and reducing [Cl-]o by a factor of 25 all rapidly depolarize the membrane and inhibit Cl- influx. Some of these treatments do not inhibit the effluxes of K+ and Na+. Increasing [K+]o also depolarizes the membrane both under normal conditions and at low temperature; in the latter case the membrane is partially depolarized in normal seawater (low [K+]o) and in high [K+]o positive potentials of up to +15 mv are attained. It is concluded that the membrane potential is controlled by the electrogenic influx of Cl-, and also, at least in some circumstances, by the diffusion of K+. In addition, it is suggested that electrogenic efflux of H+ may be important in transient nonequilibrium situations. An Appendix deals with the interpretation of simple nonsteady-state tracer kinetic data.

K+-stimulated sugar uptake in skeletal muscle: role of cytoplasmic Ca2+

1983 ◽  
Vol 245 (1) ◽  
pp. C125-C132 ◽  
Author(s):  
P. Valant ◽  
D. Erlij
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cytochalasin B ◽  
Sugar Transport ◽  
Sugar Uptake ◽  
Frog Skeletal Muscle ◽  
High K ◽  
K Concentration ◽  
External K

We have compared the effects of insulin with those of elevated external K+ concentration ([K+]o) on sugar uptake and protein synthesis by frog skeletal muscle. When [K+]o was between 0.5 and 15 mM there were no effects on uptake; however, when 20 mM was used a significant increase was observed. Further increases in [K+]o caused larger stimulations of uptake. The stimulation persisted for 2.5 h after washing the high [K+]o. The stimulations caused by both insulin and high K+ were markedly inhibited by cytochalasin B. Dantrolene nearly abolished the response to high K+, whereas it had only minor effects on the resting sugar uptake and on the stimulations caused by either insulin or epinephrine. These results suggest that while both insulin and high K+ activate the cytochalasin-sensitive transport system of sugar transport, each agent must act through a different pathway, because only the effects of high K+ were dantrolene sensitive. The effect of dantrolene suggests that the enhancement of sugar transport caused by high K+ is due to an increase of cytoplasmic Ca2+. In contrast to insulin, high K+ did not modify the rate of protein synthesis.

Electrogenic Na+ Transport in a Crustacean Coxal Receptor

1979 ◽  
Vol 78 (1) ◽  
pp. 29-45
Author(s):  
MAURIZIO MIROLLI
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Input Resistance ◽  
Scylla Serrata ◽  
Partial Action ◽  
State Response ◽  
Electrogenic Na Pump ◽  
K Concentration ◽  
Low K ◽  
In Cells

1. The response of the coxal receptors of the crab Scylla serrata to step stretches consisted of a partial action potential, Vα, followed by a steady-state depolarization, V8. The input resistance of the fibre was reduced during V8. 2. In the absence of stimulation, the dendrites of the receptors depolarized when external Na+ was substituted with choline or Li+, and when the external K+ concentration was increased or decreased. The dendrites also depolarized when ouabain was added to the saline. 3. The amplitude of both Vα and V8 was dependent on external Na+. In cells which were depolarized by ouabain, the amplitude of V8 increased when the K+ concentration of the saline was reduced. 4. V8 was followed by a small, but long-lasting, after-potential which was depolarizing when the membrane potential was between −70 and −60 mV. In cells depolarized by ouabain or by low K+ saline, the after-potential became hyperpolarizing. 5. When trains of brief stretches (each 5 ms in duration) were used as stimuli, the cells responded with trains of Vα responses. During this tetanic stimulation the cells hyperpolarized; cessation of the stimulus train was followed by a long-lasting hyperpolarization (PTH). 6. PTH was abolished in Li+ saline, in low K+ saline, and in the presence of ouabain. In control or in low K+ saline, PTH was not accompanied by a decrease in the input resistance of the fibres. 7. It is concluded that an electrogenic Na+ pump (or equivalent process) contributes a substantial fraction of the membrane potential of the unstimulated coxal receptors. Pump activity could be increased by Na+-loading the distal part of the cells with trains of Vα responses. By contrast, during the steady-state response to stretch, the pump was not activated.

scholarly journals THE EFFECT OF ENVIRONMENTAL POTASSIUM AND CALCIUM CONCENTRATIONS ON THE RECOVERY OF THE ACTION POTENTIAL AND RELATED FUNCTIONS OF NERVE

1947 ◽  
Vol 30 (6) ◽  
pp. 493-517 ◽  
Author(s):  
Helen Tredway Graham ◽  
H. A. Blair
Keyword(s):  
Critical Level ◽  
Specific Effect ◽  
The Other ◽  
Level Control ◽  
Definite Effect ◽  
High K ◽  
Low Levels ◽  
K Concentration ◽  
Low K ◽  
Frog Sciatic Nerve

1. When the Ringer's solution applied to isolated frog sciatic nerve contains K+ in concentrations greater than 2 x standard, the height of the spike and of the after-potential is decreased, as is the duration of the after-potential; recovery of height and of excitability following response is delayed; degree and duration of supernormal excitability are decreased; postcathodal depression and postanodal enhancement are increased and prolonged. 2. The nerve functions just listed in general all change in the opposite direction when exposed' to increased environmental [Ca++]. (4.5–20 x standard) or decreased [K+] (0.05–0.2 x standard). The effects of decreased [Ca++] (0.20–0.25 x standard) are indeterminate. 3. When [K+] and [Ca++] are both greater than 2 x standard, whatever the ratio between the concentrations the effects characteristic of high [K+] eventually predominate. However, these effects, except for those involving spike height, are preceded by effects characteristic of high [Ca++] when this cation is present in sufficient excess. 4. When [K+] and [Ca++] are reduced to equal low levels (0.1–0.2 x standard), effects characteristic of low [K+] and high [Ca++] are obtained. 5. The experimentally determined order of ability of the environments to produce changes characteristic of high K+ (which is the reverse of the order of their ability to produce changes characteristic of high [Ca++]), is not the order of their K+ or Ca++ concentrations, nor of the ratio between these concentrations (Table II). 6. The results may be explained by the assumption that the functions investigated are all to greater or less degree controlled by (1) the [K+]/[Ca++] ratio and (2) the K+ concentration, at least when this exceeds a critical level. Control by [K+] is more effective for spike height and its recovery after stimulation than for the other functions. The special rôle of K+ is attributed to an unknown specific effect of this ion which Ca++ is unable to oppose. It is suggested that this K+ effect in general becomes marked on the frog nerve functions investigated when the K+ concentration is somewhat above 2 x standard, while the [K+]/[Ca++] ratio must be changed by a factor of 4 or more before it exerts a definite effect on these functions. 7. In standard and in modified cationic environments, nerve functions vary in the ease with which they manifest changes characteristic of high [K+] or of high [Ca++]. 8. The after-potential functions are less completely controlled by the cationic environment than are the other functions investigated.

scholarly journals Strophanthidin-sensitive sodium fluxes in metabolically poisoned frog skeletal muscle.

1976 ◽  
Vol 68 (4) ◽  
pp. 405-420 ◽  
Author(s):  
B G Kennedy ◽  
P De Weer
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Human Erythrocyte ◽  
Sodium Pump ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Frog Skeletal Muscle ◽  
Na Efflux ◽  
Unidirectional Fluxes ◽  
External K

Strophanthidin-sensitive and insensitive unidirectional fluxes of Na were measured in fog sartorius muscles whose internal Na levels were elevated by overnight storage in the cold. ATP levels were lowered, and ADP levels raised, by metabolic poisoning with either 2,4-dinitrofluorobenzene or iodoacetamide. Strophanthidin-sensitive Na efflux and influx both increased after poisoning, while strophanthidin-insensitives fluxes did not. The increase in efflux did not require the presence of external K but was greatly attenuated when Li replaced Na as the major external cation. Membrane potential was not markedly altered by 2,4-dinitrofluorobenzene. These observations indicate that the sodium pump of frog skeletal muscle resembles that of squid giant axon and human erythrocyte in its ability to catalyze Na-Na exchange to an extent determined by intracellular ATP/ADP levels.

Solute is imported to elongating root cells of barley as a pressure driven-flow of solution

2004 ◽  
Vol 31 (4) ◽  
pp. 391 ◽  
Author(s):  
Nick Gould ◽  
Michael R. Thorpe ◽  
Peter E. H. Minchin ◽  
Jeremy Pritchard ◽  
Philip J. White
Keyword(s):  
Hydrostatic Pressure ◽  
Pressure Difference ◽  
Root Elongation ◽  
Root Cell ◽  
Root Cells ◽  
High K ◽  
K Concentration ◽  
Pressure Driven Flow ◽  
Low K ◽  
Pressure Driven

This work relates solute import to elongating root cells in barley to the water relations of the symplastic pathway under conditions of varied plant K+ status. K+ is a major constituent of phloem sieve element (SE) sap, and as an osmoticum, it is believed to have a role in maintaining SE hydrostatic pressure and thus sap flow from source to sink tissue. The hypothesis that the solute import to elongating root cells is linked to pressure driven flow from the sieve tube is examined.Plants were grown in solutions containing either 0.05 mM (low K) or 2.05 mM (high K) K+ concentration. Solute import to the root elongation zone was estimated from biomass accumulation over time accounting for respiration and root elongation rate. SE sap K+ concentration was measured using X-ray microanalyses and osmotic pressure by picolitre osmometry. SE hydrostatic pressure was measured directly with a pressure probe glued onto an excised aphid stylet. Elongating root cell hydrostatic pressure was measured using a cell pressure probe.The low-K plants had lower SE K+ concentration and SE hydrostatic pressure compared to the high-K plants, but the elongating root cell hydrostatic pressure was similar in both treatments, thus the pressure difference between the SE and elongating root cells was less in the low-K plants compared to the high-K plants.The solute import rate to elongating root cells was lower in the low K plants and the reduction could be accounted for as a pressure driven solute flux, with a reduction both in the pressure difference between root sieve elements and elongating cells, and in the sap concentration.

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