Biomaterial Database

An evaluation of the membrane constants and the potassium conductance in metabolically exhausted muscle fibres. 1976

R Fink, and H C Lüttgau

1. The membrane characteristics of metabolically poisoned and mechanically exhausted frog skeletal muscle fibres were investigated with intracellular micro-electrodes. 2. When cyanide plus iodoacetate were applied as metabolic poisons twitch tension declined towards zero after 150-300 stimuli (0-3 Hz; temperature = 0 degrees C). At the beginning of stimulation the mean resting potenial fell from -75 to -69 mV; it rose subsequently to -83 mV. The membrane resistance decreased during this stimulation period along a sigmoid time course to 4-6% of the original value. 3. In completely exhausted fibres the following membrane constants were estimated (23 degrees C): length constant, 0-31 mm; input resistance, 31 komega; membrane resistance, 58 omega.cm2. These values were calculated under the assumption of a constant internal resistivity of 170 omega. cm. The Q10 values of these constants were similar to those in normal fibres. Afew experiments revealed that the membrane capacity remained roughly constant under these conditions. 4. The current-voltage relation of exhausted fibres was approximately linear in the range between -60 and -100 mV. At less negative potentials the conductance increased slightly while at more negative potentials it decreased. The latter, in particular, became more evident when the imput current was converted into membrane current density by applying Cole's theorem. 5TEA+ and Rb+ in the external solution increased the membrane resistance of exhausted fibres by more than one order of magnitude. The major part of the membrane conductance induced by exhaustion, however, could not be blocked by these ions or Zn2+. 6. Chloride-free test solutions were used to measure the relative contributions of potassium and chloride ions to the membrane conductance. The relation GK:GC1 changed from 2:3 in normal fibres to 5:1 in exhausted ones. In absolute terms GK rose from ca. 130 to 14,300 mumho/cm2 and GC1 from ca. 200 to 2900 mumho/cm2. The discrimination between K+ and Na+ by the resting membrane in exhausted fibres was probably equal to or even higher than that under normal conditions. 7. In normal fibres the input resistance decreased by up to 20% after the external application of 1-2 mM caffeine, which is known to release calcium ions from internal stores. The elevation in internal Ca2+ by direct injection caused a small and, as a rule, irreversible decrease in input resistance which was probably partly due to local damage to the surface membrane. 8. It is concluded that in metabolically exhausted muscle fibres the surface and tubular membranes are still intact and that the observed decrease in membrane resistance is mainly due to an increase in potassium conductance. In addition, the results indicate that the gating mechanism of the potassium channels (presumably those with the characteristics of the slow component) is affected when energy reserves diminish.

UI	MeSH Term	Description	Entries
D007461	Iodoacetates	Iodinated derivatives of acetic acid. Iodoacetates are commonly used as alkylating sulfhydryl reagents and enzyme inhibitors in biochemical research.	Iodoacetic Acids,Acids, Iodoacetic
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D009132	Muscles	Contractile tissue that produces movement in animals.	Muscle Tissue,Muscle,Muscle Tissues,Tissue, Muscle,Tissues, Muscle
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.
D011896	Rana temporaria	A species of the family Ranidae occurring in a wide variety of habitats from within the Arctic Circle to South Africa, Australia, etc.	European Common Frog,Frog, Common European,Common European Frog,Common Frog, European,European Frog, Common,Frog, European Common
D002110	Caffeine	A methylxanthine naturally occurring in some beverages and also used as a pharmacological agent. Caffeine's most notable pharmacological effect is as a central nervous system stimulant, increasing alertness and producing agitation. It also relaxes SMOOTH MUSCLE, stimulates CARDIAC MUSCLE, stimulates DIURESIS, and appears to be useful in the treatment of some types of headache. Several cellular actions of caffeine have been observed, but it is not entirely clear how each contributes to its pharmacological profile. Among the most important are inhibition of cyclic nucleotide PHOSPHODIESTERASES, antagonism of ADENOSINE RECEPTORS, and modulation of intracellular calcium handling.	1,3,7-Trimethylxanthine,Caffedrine,Coffeinum N,Coffeinum Purrum,Dexitac,Durvitan,No Doz,Percoffedrinol N,Percutaféine,Quick-Pep,Vivarin,Quick Pep,QuickPep
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D003486	Cyanides	Inorganic salts of HYDROGEN CYANIDE containing the -CN radical. The concept also includes isocyanides. It is distinguished from NITRILES, which denotes organic compounds containing the -CN radical.	Cyanide,Isocyanide,Isocyanides
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia