DISCRIMINATION BETWEEN ALKALI METAL CATIONS BY YEAST. I. EFFECT OF PH ON UPTAKE

Extracellular pH markedly influences the ability of yeast cells to discriminate between K⁺ and Na⁺, with K⁺ favored to a greater degree at low pH. Studies of the kinetics of uptake of individual alkali metal cations by fermenting yeast indicate three zones relative to pH. Between pH 6 and 8, H⁺ has no effect. Below pH 4, H⁺ competitively inhibits the transport of each cation. Between pH 4 and 6, H⁺ acts kinetically as a predominantly non-competitive inhibitor. Both effects can be reversed by increasing the concentrations of cations. However, the concentrations required to reverse the competitive effect are considerably lower than those required to reverse the apparently non-competitive effect. It is suggested that H⁺ and the alkali metal cations can combine with two sites, a transport or carrier site, and a second, non-transporting site that influences the maximal rate of transport. Because the non-competitive inhibitory effect of H⁺ is considerably greater on the other cations than on K⁺, the discrimination in favor of K⁺ is increased severalfold at low pH, beyond that predicted on the basis of the relative affinities for the transport site.

BUFFER DISTRIBUTION IN ISOLATED PERFUSED RAT HEART MEASURED BY RUBIDIUM 86

The pattern of distribution of Rb86 in sections of the isolated perfused heart was determined as a measure of uniformity of coronary artery flow. Results suggest that coronary flow was uniform after nonrecirculated perfusion for 15 min. Similar results were obtained in hearts perfused for 30 and for 60 min. The distribution of Rb86 was comparable in hearts perfused for 30 min with perfusate circulated through either coarse porosity, sintered-glass filters or 5-µ Millipore filters. A nonuniform distribution of isotope was demonstrated with ligation of branches of coronary arteries and with the introduction of air. The results suggest that hearts perfused by recirculation of buffer through coarse porosity, sintered-glass filters have a uniform distribution of perfusate throughout the heart.

THE EFFECT OF MUCOSAL AND SEROSAL SOLUTION CATIONS ON BIOELECTRIC PROPERTIES OF THE ISOLATED TOAD BLADDER

The spontaneous transtissue potential and the DC conductance of the isolated toad bladder were measured when the tissue was exposed to sulfate Ringer's solutions of modified ionic composition. Na(+) was replaced to varying extents by (C(2)H(5))(3)NH(+), (C(2)H(5))(4)N(+), Li(+), Cs(+), K(+), or Rb(+). Reversible and irreversible changes were observed. The reversible changes were consistent with equations derived from the Nernst-Planck diffusion equation, and gave the following functional description of the bladder: (a) the potential measurements were compatible with two membranes in series; (b) the mucosal surface was more permeable to Na(+) than to other monovalent cations; (c) the serosal surface was permeable to both K(+) and Na(+) but preferentially to K(+); (d) the rate of Na(+) diffusion across the mucosal membrane appeared to approach a maximum but two alternative interpretations are discussed; (e) the conductance data were consistent with the assumption of a constant concentration gradient for the penetrating ions within the membrane (Henderson's assumption) provided suitable hypotheses are made concerning the Na(+) distribution between the membrane surfaces and the bulk phases of the adjacent solutions; (f) the conductance and spontaneous potential data suggested that the mucosal membranes of a small fraction of the epithelial cells were more permeable than the mucosal membranes of the majority of these cells. The irreversible changes were almost entirely associated with cation substitution in the serosal solution. However, Li(+) produced an irreversible fall in voltage when added to either side of the tissue.

EFFECT OF ALKALI METAL CATIONS ON THE POTENTIAL ACROSS TOAD AND BULLFROG URINARY BLADDER

Isolated urinary bladders of the bullfrog (R. catesbeiana) and the toad (B. marinus) were mounted in an Ussing chamber. Potential differences up to 114 mv were observed in bullfrog bladder when the mucosal surface was bathed in dilute Na₂SO₄ and the serosal surface in sulfate Ringer's. In experiments with bullfrogs, K was used to replace Na in the mucosal solution and Na was used for K in the serosal solutions. The selectivity was judged in terms of the relative effectiveness of the replacement cation in maintaining the bladder potential. In experiments with toads, K and Rb were equally poor replacements for Na at the mucosal border, while Rb was a good replacement for K at the serosal border. Li in the mucosal solution appeared to depress the potential in part irreversibly. At the serosal border, Li was a partially effective substitute for K, more so than was Na. However, both were poor replacements compared to Rb. The mucosal surface of the urinary bladder of both frog and toad appears to be Na-selective and the serosal surface appears to be K-selective, consistent with the Koefoed-Johnsen-Ussing model for frog skin.

GRAMICIDIN AND ION TRANSPORT IN ISOLATED LIVER MITOCHONDRIA

1. Gramicidin caused H(+) production by liver mitochondria; this process was dependent on the presence of Na(+), Li(+), Rb(+) or Cs(+). In the presence of one of these alkali-metal ions and phosphate, gramicidin caused mitochondrial swelling and increased oxygen consumption. 2. Uncoupling agents, anaerobic conditions or respiratory inhibitors both inhibited and reversed H(+) production and swelling. Both these processes could be supported by coupled electron transport through even a restricted portion of the respiratory chain. 3. NH(4) (+) also caused stimulation of respiration in the presence of gramicidin. In this case phosphate was not required. NH(4) (+), in the presence of gramicidin, caused contraction of the mitochondria and a reversal of K(+)-induced swelling and H(+) production. 4. Uncoupling agents or NH(4) (+) together with gramicidin caused the release of Sr(2+) that had been accumulated by mitochondria in the presence of phosphate. 5. These results are discussed in relation to a postulated respiration-dependent H(+) pump located in the mitochondrial membrane. It is suggested that gramicidin allows alkali-metal ions to pass through the mitochondrial membrane.

THE EFFECTS OF ALKALI METAL CATIONS AND COMMON ANIONS ON THE FROG SKIN POTENTIAL

The effects on the potential difference across isolated frog skin (R. catesbeiana, R. pipiens) of changing the ionic composition of the bathing solutions have been examined. Estimates of mean values and precision are presented for the potential changes produced by substituting other alkali metal cations for Na at the outside border and for K at the inside border. In terms of ability to mimic Na at the outside border of bullfrog skin, the selectivity order is Li > Rb, K, Cs; at the outside border of leopard frog skin, Li > Cs, K, Rb. In terms of ability to mimic K at the inside border of bullfrog and leopard frog skin: Rb > Cs > Li > Na. Orders of anion selectivity in terms of sensitivity of the potential for the outside border of bullfrog skin are Br > Cl > NO(3) > I > SO(4), isethionate and of leopard frog skin are Br, Cl > I, NO(3), SO(4). An effect of the solution composition (ionic strength?) on the apparent Na-K selectivity of the outside border is described. The results of the investigation have been interpreted and discussed in terms of the application of the constant field equation to the Koefoed-Johnsen-Ussing frog skin model. These observations may be useful in constructing and testing models of biological ionic selectivity.

THE EFFECTS OF VARIOUS IONS ON RESTING AND SPIKE POTENTIALS OF BARNACLE MUSCLE FIBERS

Effects of monovalent cations and some anions on the electrical properties of the barnacle muscle fiber membrane were studied when the intra- or extracellular concentrations of those ions were altered by longitudinal intra-cellular injection. The resting potential of the normal fiber decreases linearly with increase of logarithm of [K⁺]_out and the decrement for a tenfold increase in [K⁺]_out is 58 mv when the product, [K⁺]_out ·[Cl^-]_out, is kept constant. It also decreases with decreasing [K⁺]_in but is always less than expected theoretically. The deviation becomes larger as [K⁺]_in increases and the resting potential finally starts to decrease with increasing [K⁺]_in for [K⁺]_in > 250 mM. When the internal K⁺ concentration is decreased the overshoot of the spike potential increases and the time course of the spike potential becomes more prolonged. In substituting for the internal K⁺, Na⁺ and sucrose affect the resting and spike potentials similarly. Some organic cations (guanidine, choline, tris, and TMA) behave like sucrose while some other organic cations (TEA, TPA, and TBA) have a specific effect and prolong the spike potential if they are applied intracellularly or extracellularly. In all cases the active membrane potential increases linearly with the logarithm of [Ca⁺⁺]_out/[K⁺]_in and the increment is about 29 mv for tenfold increase in this ratio. The fiber membrane is permeable to Cl^- and other smaller anions (Br^- and I^-) but not to acetate^- and larger anions (citrate^-, sulfate^-, and methanesulfonate^-).