Biomaterial Database

Investigation of factors affecting the intracellular sodium activity in the smooth muscle of guinea-pig ureter. 1987

C C Aickin

University Department of Pharmacology, Oxford.

1. The intracellular Na+ activity (aNai) of the smooth muscle cells from guinea-pig ureter has been measured using double-barrelled Na+-sensitive micro-electrodes. aiNa in modified Krebs solution at 35 degrees C was of a mean 7.4 +/- 2.9 mM (n = 32, S.D. of an observation), equivalent to a Na+ equilibrium potential (ENa) of +66.7 mV. Membrane potential (Em) was of a mean -50.8 +/- 4.6 mV. 2. Inhibition of the Na+ pump by application of ouabain or removal of external K+ (K+o) resulted in a restricted rise of aNai. The rate of rise was faster in the presence of ouabain (10(-4) M) but the stabilized aNai was not significantly different from that observed after the prolonged absence of K+o. The mean aiNa recorded after prolonged Na+ pump inhibition was 20.6 +/- 5.5 mM (n = 28), equivalent to an ENa of +39.6 mV. Neither removal of K+o after aNai had stabilized in the presence of ouabain nor application of ouabain after aNai had stabilized in K+-free solution caused a rise in aiNa, suggesting that the Na+ pump was fully inhibited by either procedure. 3. Reduction of Na+o resulted in a rapid fall in aiNa against the electrochemical gradient, both before and after Na+ pump inhibition. At each level of Na+o, aNai stabilized such that ENa remained approximately constant in either condition. Readdition of Na+o resulted in a rapid recovery of aNai. 4. Elevation of Ca2+o (at constant Na+o) caused a fall in aNai of much the same time course as that observed on reduction of Na+o, both before and after Na+ pump inhibition. The extent of the fall was dependent upon the initial aNai. Reduction of Ca2+o resulted in a rise in aNai. 5. Elevation of the external divalent cation concentration with Mn2+ or, to a lesser extent, Mg2+ reduced aiNa in the presence of a functional Na+ pump. But after prolonged exposure to ouabain or K+-free solution, elevation of Mg2+o had no effect on aiNa while application of Mn2+o caused a slow rise. These results suggest that Ca2+o affects aiNa in two ways. One is mimicked by Mg2+ and Mn2+ and is probably due to alteration of the Na+ leak. The other is a specific effect, revealed by Na+ pump inhibition. 6. It is concluded that aiNa can be maintained far from equilibrium in the absence of a functional Na+ pump. Several lines of evidence are discussed which indicate the participation of Na+-Ca2+ exchange in Na+ extrusion in this condition.

UI	MeSH Term	Description	Entries
D007473	Ion Channels	Gated, ion-selective glycoproteins that traverse membranes. The stimulus for ION CHANNEL GATING can be due to a variety of stimuli such as LIGANDS, a TRANSMEMBRANE POTENTIAL DIFFERENCE, mechanical deformation or through INTRACELLULAR SIGNALING PEPTIDES AND PROTEINS.	Membrane Channels,Ion Channel,Ionic Channel,Ionic Channels,Membrane Channel,Channel, Ion,Channel, Ionic,Channel, Membrane,Channels, Ion,Channels, Ionic,Channels, Membrane
D008297	Male		Males
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
D009130	Muscle, Smooth	Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. (From Stedman, 25th ed)	Muscle, Involuntary,Smooth Muscle,Involuntary Muscle,Involuntary Muscles,Muscles, Involuntary,Muscles, Smooth,Smooth Muscles
D010042	Ouabain	A cardioactive glycoside consisting of rhamnose and ouabagenin, obtained from the seeds of Strophanthus gratus and other plants of the Apocynaceae; used like DIGITALIS. It is commonly used in cell biological studies as an inhibitor of the NA(+)-K(+)-EXCHANGING ATPASE.	Acocantherin,G-Strophanthin,Acolongifloroside K,G Strophanthin
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.
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
D002413	Cations, Divalent	Positively charged atoms, radicals or groups of atoms with a valence of plus 2, which travel to the cathode or negative pole during electrolysis.	Divalent Cations
D006168	Guinea Pigs	A common name used for the genus Cavia. The most common species is Cavia porcellus which is the domesticated guinea pig used for pets and biomedical research.	Cavia,Cavia porcellus,Guinea Pig,Pig, Guinea,Pigs, Guinea
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential