[Dependence of the electric resting potential of isolated perfused mammalian muscles on extracellular potassium concentration]

Measurements of electrical potential differences on single nephrons of the perfused Necturus kidney

Stable electrical potential differences can be measured by means of conventional glass microelectrodes across the cell membrane of renal tubule cells and across the epithelial wall of single tubules in the doubly perfused kidney of Necturus. These measurements have been carried out with amphibian Ringer's solution, and with solutions of altered ionic composition. The proximal tubule cell has been found to be electrically asymmetrical inasmuch as a smaller potential difference is maintained across the luminal cell membrane than across the peritubular cell boundary. The tubule lumen is always electrically negative with respect to the peritubular extracellular medium. Observations on the effectiveness of potassium ions in depolarizing single tubule cells indicate that the transmembrane potential is essentially an inverse function of the logarithm of the external potassium concentration. The behavior of the peritubular transmembrane potential resembles more closely an ideal potassium electrode than that of the luminal transmembrane potential. From these results, and the effects of various ionic substitutions on the electrical profile of the renal tubular epithelium, a thesis concerning the origin of the observed potential differences is presented. A sodium extrusion mechanism is considered to be located at the peritubular cell boundary, and reasons are given for the hypothesis that the electrical asymmetry across the proximal renal tubule cell could arise as a consequence of differences in the relative sodium and potassium permeability at the luminal and peritubular cell boundaries.

Insulin action on membrane potential and glucose uptake: effects of high potassium

These experiments were designed to test the hypothesis that insulin-induced hyperpolarization is a link in the chain of events leading to stimulation of glucose transport. External potassium concentration, [K+]o, was increased by equimolar substitution of KCl for NaCl, a method known to cause cell swelling, and by substitution of [K+]o for [Na+]o with maintenance of constant [K+]o X [Cl-]o product, a method that does not cause cell swelling. When there was constant KCl product, even at 76.8 meq [K+]o insulin continued to hyperpolarize, although by only approximately 44% as much as in normal [K+]o, and insulin-stimulated 2-deoxyglucose uptake was only approximately 60% of that at normal [K+]o. With equimolar substitution of KCl for NaCl: electrical potential difference across cell membranes of surface fibers of rat caudofemoralis muscle decreased with logarithm [K+]o, in the presence or absence of insulin. Insulin-induced hyperpolarization decreased as [K+]o increased and disappeared at 36 mM [K+]o. The amount of insulin bound to its receptors in 1 h was not affected by [K+]o over the range studied. Insulin effects on membrane potential and on 2-deoxyglucose uptake, as both were altered by [K+]o, correlated well. As the probe moved in depth through the first six fibers there was stepwise decrease in depolarization in high [K+]o in the absence of insulin. Insulin hyperpolarized the deepest of these fibers, even when it did not hyperpolarize the outermost. The decrease in insulin-induced hyperpolarization as [K+]o increases is consistent with the hypothesis that insulin hyperpolarizes by decreasing the ratio PNa/PK.

Transmembrane potentials in guinea-pig hepatocytes

1. In pieces of guinea-pig liver with an intact capsule, the mean resting potential (E) is -49.8 mV, close to the value for in vivo hepatocytes and significantly higher than a similar preparation of rat liver. E is considerably less than the calculated K equilibrium potential of about -90 mV.2. Changes in [K(+)](o) in the range of 0-10 mM produce almost no change in E. At [K(+)](o) above 20 mM, a tenfold increase produces only a 33 mV depolarization. The results with changing [K(+)](o) are the same in Cl(-) free solutions (isethionate substitution) or when the [K(+)](o)[Cl(-)](o) product is kept constant. E rapidly returned to normal in liver pieces returned to Ringer after prolonged soaking in high K(+) solution.3. Changes in [Na(+)](o), [Cl(-)](o), [H(+)](o), [Ca(2+)](o) or [Mg(2+)](o) have little effect on E. Simultaneous variation of [Na(+)](o) and [Cl(-)](o) in opposite directions to maximize predicted changes in E also has only a minimal effect on E.4. Cyanide (5 mM) or ouabain (10(-4)M) cause depolarization, so there is no reason to believe that pumps sensitive to these poisons are normally lowering resting potential. Part of the normal E may be produced by an electrogenic ouabain-sensitive ion pump.5. The data is interpreted by using a form of the constant field equation developed by Brading & Caldwell (1971). Application of this method yields P(Na)/P(K) less than 0.04, P(Cl)/P(K) approximately 0.3. Additional terms, x and y, are required to account for the behaviour of E. Their physical basis remains undetermined.6. Suggestions are presented for further study and for the application of the method of Brading & Caldwell to other non-excitable cells and to excitable cells in low [K(+)](o), in which E is poorly understood.

Measurement of intracellular pH of skeletal muscle with pH-sensitive glass microelectrodes

We used three methods to examine the relationship among intracellular pH, transmembrane potential, and extracellular pH. Single-barreled electrodes permitted the determination of resting potential and intracellular pH with a minimum of cellular injury. Double-barreled electrodes, which incorporated a reference as well as a pH-sensitive electrode in a single tip, facilitated the direct measurement of intracellular pH without the interposition of the transmembrane potential. Triple-barreled electrodes permitted measurement of intracellular pH during the controlled hyperpolarization or depolarization of the cell membrane. The results of all three methods were in close agreement and disclosed that the H(+) activity of intracellular and extracellular fluid is in electrochemical equilibrium at any given transmembrane potential. This implies that the determinants of intracellular pH are the transmembrane potential and the blood pH. The actual pH of the normal resting muscle cell is 5.99, as estimated from the normal transmembrane potential and blood pH, or as determined by direct measurements of intracellular pH.