The cation specificity of the potassium and gramicidin channels of muscle fiber membrane

Conductance ratios (Gi/Gk) and permeability ratios (Pi/Pk) for monovalent cations in frog muscle fibres have been defined under constant current conditions using a double sucrose gap method. Selectivity determined from potassium channel conductance is: K+ greater than Rb+ greater than Cs+ greater than greater than NH4+ greater than Na+ greater than Li+. In gramicidin channels both the permeability and conductance sequences are identical: NH4+ greater than Cs+ greater than Rb+ greater than K+ greater than Na+ greater than Li+. In isotonic K+-sulfate solution with one-sided addition of external [Tl+] (2.5 x 10(-3)-20 x 10(-3) M), differences in the conductance and permeability ratios for gramicidin channel were observed.     

Structure-activity relationships among noncyclic dicarboxamide Li(+)-selective carriers studied in lipid bilayer membranes.

The structure-activity relationships among three noncyclic diimide ionophores, designed to be Li+ carriers, were studied in lipid bilayer membranes. These ionophores (ETH1644, ETH1810, and ETH1811) vary in their N-imide substituents, going from two isobutyls to one isobutyl and one cyclohexyl to two cyclohexyls, respectively. ETH1811 was found to form two types of complexes with 1:1 and 1:2 ion-carrier stoichiometries, the former type dominant over most of the ionophore (0.1-10 microM) and salt (0.01-1.0 M) concentration ranges studied. In contrast, ETH1644 and ETH1810 were previously found to form a single type of complex with the 1:2 stoichiometry. The alkali cations selectivity sequence induced by ETH1811 is Li+ (1) greater than Na+ (0.08) greater than K+ (0.02) greater than Cs+ (0.008). These ETH1811-induced ionic selectivites as well as its relative potency in ion transport were found to be inferior to those of ETH1644 and ETH1810 (the latter being the best in this series). The conductance-voltage relationships reported here, for all three ionophores transporting alkali cations, were found to fit with a transport mechanism in which the diffusion of the ion-ionophore complex across the membrane is the single rate-limiting step, with the following exceptions: The addition of the dissociation of the ion-carrier complex as a second rate limiting step, for the Li(+)-ETH1810 and the Li(+)-ETH1811 systems. For ETH1810 the kinetics of the dissociation step is a minor, whereas for ETH1811 case it is a significant, addition (the ratio of the diffusion to dissociation rate constants being 0.08 and 0.2, respectively). The implications of the effects of the continuous structural change of these ionophores on their performance as ion carriers and on the design and synthesis of improved Li(+)-selective ionophores are discussed.     

Monovalent ion current through single calcium channels of skeletal muscle transverse tubules.

Akali monovalents, Li, Na, K, Cs, and organic monovalents of molecular cross section less than 20 A2, ammonium, methylammonium, hydrazinium, guanidinium, are shown to have a measurable conductance through Ca channels of muscle transverse tubules reconstituted into planar bilayers. For the alkali series, single channel conductances follow the sequence Cs approximately equal to K greater than Na greater than Li with a conductance ratio [g(Cs)/g(Li)] = 1.7. For permeability ratios, the sequence is Li greater than Na greater than K approximately equal to Cs with [P(Li)/P(Cs)] = 1.5. Monovalent current is only unmasked when Ba ions are not present. In mixtures of Cs and Ba, single channel current reverses close to the Ba equilibrium potential and more than 100 mV away from the Cs equilibrium potential. A cutoff in conduction is found for organic cations larger than trimethylammonium; this suggests an apparent pore aperture of about 5 X 5 A. Even in such a large pore, the fact that the alkali cation permeability sequence and conductance sequence are inverted rules out molecular sieving as the mechanism of selection among monovalents.     

Ion transport mediated by the valinomycin analogue cyclo(L-Lac-L-Val-D- Pro-D-Val)3 in lipid bilayer membranes

Cyclo(L-Lac-L-Val-D-Pro-D-Val)3 (PV-Lac) a structural analogue of the ion-carrier valinomycin, increases the cation permeability of lipid bilayer membranes by forming a 1:1 ion-carrier complex. The selectively sequence for PV-Lac is identical to that of valinomycin; i.e., Rb+ greater than K+ greater than Cs+ greater than or equal to NH+4 greater than Na+ greater than Li+. The steady-state zero-voltage conductance, G(0), is a saturating function of KCl concentration. A similar behavior was found for Rb+, Cs+, and NH+4. However, the ion concentration at which G(0) reaches a plateau strongly depends on membrane composition. The current-voltage curves present saturating characteristics, except at low ion concentrations of Rb+, K+, or Cs+. The ion concentration at which the saturating characteristics appear depends on membrane composition. These and other results presented in this paper agree with a model that assumes complexation between carrier and ion at the membrane-water interface. Current relaxation after voltage-jump studies were also performed for PV-Lac. Both the time constant and the amplitude of the current after a voltage jump strongly depend on ion concentration and membrane composition. These results, together with the stationary conductance data, were used to evaluate the rate constants of the PV-Lac-mediated K+ transport. In glycerolmonooleate they are: association rate constant, 2 x 10(6) M-1 s-1; dissociation rate constant, 4 x 10(5) s-1; translocation rate constant for complex, 5 x 10(4) s-1; and the rate of translocation of the free carrier (ks), 55 s-1. ks is much smaller for PV-Lac than for valinomycin and thus limits the efficiency with which the carrier is able to translocate cations across the membrane.     

Effect of the alkaline cations on the stability of the model polynucleotide poly(dG-dC)·poly(dG-dC)

When the model polynucleotide poly(dG-dC)?poly(dG-dC) [polyGC] is titrated with a strong acid (HCl) in unbuffered aqueous solutions containing the chlorides of the alkali metals in the concentration range 0.010?M-0.600?M, two transitions in the absorbance vs. pH plots are evidenced, characterized by the constants pK(a(?)) and pK(a(?)). The limiting values at infinite saline concentrations of these two constants, namely pK(∞)(a(?)) and pK(∞)(a(?)) obtained making use of the "one site saturation constant" equation or, in turn, of the double logarithmic plot: pK(a) vs. log([salt]?1), exhibit a clear dependence on the nature of the cations. The effects of the different alkali cations on the pK(∞)(a) values follow the Hofmeister series. In fact, the pK(∞)(a(?)) and the pK(∞)(a(?)) values are smaller for Li+ and Na+ than for Rb+ and Cs+, with K+ at the border between the two, showing that the transitions require higher concentrations of protons to occur in the presence of high concentrations of the cosmotropic ions.     

Interaction of immobilized DNA with alkaline metal and ammonium ions

Ion exchangers with various capacities (0.1-0.2 mg-equiv/g of dry gel) are synthesized by means of immobilization of DNA in polyacrylamide gel. Exchanges of alkali metal cations and ammonium are studied on these exchangers and selectively coefficients are determined. The following selectivity series of immobilized DNA in reference to the above-mentioned cations is stated: Li+ greater than or equal to NH4+ greater than or equal to Cs+ greater than Rb+ greater than K+ greater than or equal to Na+. The peculiar properties of Li+ and NH4+ in this series are noted and a possible explanation of this fact is offered. A supposition regarding the reduced activity of water in the polyacrylamide gel containing DNA is made.     

1H, 7Li and 133Cs multicomponent self-diffusion NMR study on ion binding of Li+ and Cs+ to nucleotides and aggregation of nucleotides in aqueous solution

The Fourier transform NMR pulsed-gradient spin-echo self-diffusion technique was used for studies of nucleotides (AMP, CMP, GMP and UMP) with Li+ or Cs+ added, in 2H2O. 1H-, 7Li- and 133Cs-NMR-based self-diffusion data on the constituents provide a picture of both the degree of ion binding to nucleotides and the self-association of nucleotides in aqueous solution. Self-diffusion coefficients were investigated in a concentration range up to 0.3 molal nucleotide in 2H2O, while keeping the metal ion concentration of Li+ or Cs+ at twice the nucleotide concentration throughout the investigations. The self-association studies reveal that the aggregation constants of the Li salts differ only slightly from the corresponding constants for the disodium salts of the mononucleotides. Within a two-site bound-free model for the counterions and a cooperative indefinite aggregation model for the nucleotides one finds that the degree of ion binding for all these nucleotide systems remains approximately constant, in spite of increasing aggregate concentration. This corresponds to the well-known polyelectrolyte ion condensation behaviour, indicating that large aggregates are formed, supporting previous findings by the present authors on the aggregation behaviour of nucleotides. An observed large effect on the 17O relaxation of water in nucleotide systems can only be reconciled with the presence of relatively large aggregates in solution.     

Interaction of sodium and potassium ions with Na+,K+-ATPase. II. General properties of ouabain-sensitive K+ binding

General properties of ouabain-sensitive K+ binding to purified Na+,K+-ATPase [EC 3.6.1.3] were studied by a centrifugation method with 42K+. 1) The affinity for K+ was constant at pH values higher than 6.4, and decreased at pH values lower than 6.4. 2) Mg2+ competitively inhibited the K+ binding. The dissociation constant (Kd) for Mg2+ of the enzyme was estimated to be about 1 mM, and the ratio of Kd for Mg2+ to Kd for K+ was 120 : 1. The order of inhibitory efficiency of divalent cations toward the K+ binding was Ba2+ congruent to Ca2+ greater than Zn2+ congruent to Mn2+ greater than Sr2+ greater than Co2+ greater than Ni2+ greater than Mg2+. 3) The order of displacement efficiency of monovalent cations toward the K+ binding in the presence or absence of Mg2+ was Tl+ greater than Rb+ greater than or equal to (K+) greater than NH4+ greater than or equal to Cs+ greater than Na+ greater than Li+. The inhibition patterns of Na+ and Li+ were different from those of other monovalent cations, which competitively inhibited the K+ binding. 4) The K+ binding was not influenced by different anions, such as Cl-, SO4(2-), NO3-, acetate, and glycylglycine, which were used for preparing imidazole buffers. 5) Gramicidin D and valinomycin did not affect the K+ binding, though the former (10 micrograms/ml) inhibited the Na+,K+-ATPase activity by about half. Among various inhibitors of the ATPase, 0.1 mM p-chloromercuribenzoate and 0.1 mM tri-n-butyltin chloride completely inhibited the K+ binding. Oligomycin (10 micrograms/ml) and 10 mM N-ethylmaleimide had no effect on the K+ binding. In the presence of Na+, however, oligomycin decreased the K+ binding by increasing the inhibitory effect of Na+, whether Mg2+ was present or not. 6) ATP, adenylylimido diphosphate and ADP each at 0.2 mM decreased the K+ binding to about one-fourth of the original level at 10 microM K+ without MgCl2 and at 60 microM K+ with 5 mM MgCl2. On the other hand, AMP, Pi, and p-nitrophenylphosphate each at 0.2 mM had little effect on the K+ binding.     

Effects of alkali cations on the nuclear magnetic resonance intensity of 23Na in rat liver homogenate.

Effects of alkali cations on the nuclear magnetic resonance intensity of 23Na were studied in rat liver homogenate. The loss in the resonance intensity of 23Na in the homogenate was able to be divided into two components, one of which is abolished by the addition of Cs+ ("Cs-sensitive component"), the other being insensitive to Cs+ ("Cs-insensitive component"). Both components were sensitive to guanidinium ion. In a pH range of 7.4-4.9, the Cs-sensitive component varied remarkably, but the Cs-insensitive component remained virtually unchanged. The sequence of effectiveness of alkali cations (300 mmol/kg sample) in restoring the fractional intensity of 23Na was: Cs approximately Na greater than Li approximately Rb greater than K. It was suggested that the sequences of effectiveness of alkali cations in abolishing the two components are quite different from each other. The present results were examined within the framework of a simple model. Within this framework, the results suggest that there occur, in particulate fractions, sites whose affinity for Cs+ is sufficiently lower than that for Na+.     

The mechanism for the exclusion of sugars from the water in a model of the liveing cell: the ion-exchange resin: pore size or water structure?

The equilibrium distribution coefficients (p-value) of D-arabinose between the water in sulfonate ion-exchange resin and the external aqueous solution vary with the nature of the five alkali metal counterions studied. The strongest exclusion (lowest p-value) is found in the Li+ resin and the least exclusion (highest p-value) in the Cs+ resin. The p-value decreases with the increasing atomic weights for the alkali-metal ions: pCs+ greater than or equal to pRb+ greater than or equal to pRb+ greater than or equal to pK+ greater than pNa+ greater than pLi+. The water contents of these resins, on the other hand, vary in the opposite direction, being highest for the Li+ resin and lowest for the Cs+ resin. These data disprove the pore size theory but fully substantiate the predictions of the association-induction hypothesis.     

Symmetry and asymmetry of permeation through toxin-modified Na+ channels.

Single Na+ channels from rat skeletal muscle were inserted into planar lipid bilayers in the presence of either 200 nM batrachotoxin (BTX) or 50 microM veratridine (VT). These toxins, in addition to their ability to shift inactivation of voltage-gated Na+ channels, may be used as probes of ion conduction in these channels. Channels modified by either of the toxins have qualitatively similar selectivity for the alkali cations (Na+ approximately Li+ greater than K+ greater than Rb+ greater than Cs+). Biionic reversal potentials, for example, were concentration independent for all ions studied. Na+/K+ and Na+/Rb+ reversal potentials, however, were dependent on the orientation of the ionic species with respect to the intra- or extracellular face of the channel, whereas Na+/Li+ biionic reversal potentials were not orientation dependent. A simple, four-barrier, three-well, single-ion occupancy model was used to generate current-voltage relationships similar to those observed in symmetrical solutions of Na, K, or Li ions. The barrier profiles for Na and Li ions were symmetric, whereas that for K ions was asymmetric. This suggests the barrier to ion permeation for K ions may be different than that for Na and Li ions. With this model, these hypothetical energy barrier profiles could predict the orientation-dependent reversal potentials observed for Na+/K+ and Na+/Rb+. The energy barrier profiles, however, were not capable of describing biionic Na/Li ion permeation. Together these results support the hypothesis that Na ions have a different rate determining step for ion permeation than that of K and Rb ions.     

Calcium-binding of Synaptosomes isolated from rat brain cortex. II. Inhibitory effects of magnesium ions and some other cations.

As in our previous report (Kamino, Uyesaka & Inouye, J. Membrane Biol. 17:13 1974), the absorbance changes of murexide caused by Ca2+ and followed up by a dual wavelength spectrophotometer were applied to measure synaptosomal Ca2+-binding in the presence of cations such as Rb+, Mn2+ or La3+. All the cations tested showed a significant inhibition of synaptosomal Ca2+-binding except Li+. The inhibitory effects could be divided into the following three categories: (1) noncompetive, co-operative K+-type, which includes alkali metal ions. The potency of inhibition is K+ greater than Rb+ greater than Cs+ greater than Li+, Na+ =0; (2) competitive Mn2+ -type which includes many divalent cations. The inhibitory potency was found to be in the following order: Mn2+ greater than Sr2+ greater than Cd2+, Ba2+ greater than Mg2+; (3) nonspecific, noncompetitive La3+ -type; among the cations tested, La3+ and Ce3+ were found to markedly reduce the Ca-binding capacity of synaptosomal particles, resulting in a noncompetitive inhibition, at least in the range of Ca2+ concentration used.     

Fast single-channel measurements resolve the blocking effect of Cs+ on the K+ channel.

The Cs+ block of K+ channels has often been investigated by methods that allow only indirect estimation of the rate constants of blocking and re-opening. This paper presents single-channel records with high temporal resolution which make the direct observation of the fast transitions between the blocked and the unblocked state possible. The rate constants kOGb, kGbO of Cs(+)-dependent blocking and of re-opening are evaluated from the time constants found in the open-time and closed-time histograms. The blocking rate constant kOGb between 1000 and 50000 s-1 depends linearly on the Cs+ concentration and strongly on voltage, increasing by a factor of 1.44 per 10 mV hyperpolarization. The re-opening rate constant kGbO approximately 30000 s-1 is independent of Cs+ concentration and only slightly voltage-dependent. Formally, the results can be described by a Woodhull-model. The strong voltage dependence with d > 1, however, weakens its plausibility. The results are interpreted in terms of a molecular framework emerging from recent results on the structure of voltage-gated channels.     

The modifications of the final stages of the complement reaction by alkali metal cations.

We studied the effects of alkali metal cations on the terminal stages of complement lysis of human and sheep HK erythrocytes. Sensitized erythrocytes (EA) were reacted with limited amounts of complement for 1 hr at 37 degrees C in buffer containing 147 mM NaCl (Na buffer), which resulted in 10-40% lysis. The unlysed cells were washed with Na buffer at 0-2 degrees C and incubated for 1 hr at 37 degrees C in buffers containing 147 mM of the various alkali metal cations. Although additional lysis (25 to 65%) occurred with K, Rb, or Cs buffer, only minor degrees developed with Na or Li buffer, only minor degrees developed with Na or Li buffer. Intermediate levels occurred with 100 mM of the divalent alkali cations. Halogen ions and SCN-(147 MM), Ca++ (0.15mM), and Mg++ (0.5 mM) did not alter the effect of the alkali metal cations. Lysis occurring in K+, Rb+ or Cs+ proceeded without lag, was temperature dependent with an optimum of 43 degrees C, and had a pH optimum of 6.5. Lysis in K and Na buffers was unaffected by 10(-3) to 10(-5) M ouabain. Experiments with mixtures of cations indicated that Na+ had a mild inhibitory effect that could be totally overcome by K+, partially by Rb+, and not at all by Cs+. Li+ had a strong inhibitory effect, 6 X 10(-5) M causing 50% inhibition in buffers containing 147 mM K+, Rb+, or Cs+. By using intermediate complexes of EA and purified complement components we demonstrated that K+ enhances the lytic action of C8 on EAC1-7 as well as that of C9 on EAC1-8. It was known that Li+ facilitates lysis when acting on the entire complement reaction. We found that Li+ enhanced the lytic action of C8 on EAC1-7, with a kinetic that differed from that of the K+ effect. In addition, Li+ inhibited the enhancing effect of K+ upon lysis of EAC1-8 by C9. This occurred at concentration of Li+ similar to those which inhibited the additional lysis by K+, Rb+, and Cs+ of cells that were pretreated in Na buffer with the entire complement sequence. We propose that the major effects of alkali metal cations on complement lysis are due to their interaction with C8 and/or membrane constitutes.     

Interactions of metal ions with mu-monothiopyrophosphate.

mu-Monothiopyrophosphate (MTP) binds monovalent and divalent metal ions with dissociation constants (Kd) similar to those for pyrophosphate (PPi). The values of Kd for metal-MTP complexes are the following, as measured kinetically in the hydrolysis of MTP (microM): Mg2+, 32 +/- 4; Mn2+, 5.4 +/- 1.4; and Co2+, 27 +/- 15. The thermodynamically measured (EPR) values for Mg2+ and Co2+ are 28 +/- 13 microns and 11 +/- 4 microM, respectively; and the Kd for the complex MnPPi is 3.4 +/- 0.5 microM. The metal-MTP complexes undergo hydrolysis at rates modestly faster or slower than the rate at which MTP itself reacts. The complexes MgMTP2-, CoMTP2-, and MnMTP2- undergo hydrolytic cleavage with release of thiophosphate with observed first-order rate constants of 1.6 x 10(-2) min-1, 2.3 x 10(-2) min-1, and 0.6 x 10(-2) min-1, respectively, at 35 degrees C, compared with 1.1 x 10(-2) min-1 for MTP4- under the same conditions. Alkali metal cations also stimulate or retard the hydrolysis of MTP. At 25 degrees C and pH 12.2, the observed rate constant for tetramethylammonium MTP4- is 2.1 x 10(-3) min-1, and the estimated rate constants (min-1) for saturating alkali metals under the same conditions are as follows: Li+, 0.25 x 10(-3); Na+, 3.9 x 10(-3), K+, 6.7 x 10(-3); and Cs+, 6.7 x 10(-3). Divalent metal ions markedly retard the hydrolysis of MTP at pH 7 and 8 because complexation shifts the pH rate profile more than 2 pH units toward the acid side.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the self-association properties of the 5'-triphosphates of inosine (ITP), guanosine (GTP), and adenosine (ATP). Further evidence for ionic interactions in the highly stable dimeric [H2(ATP)]2(4-) stack

The concentration dependence of the chemical shifts for the hydrogens H-2, H-8 and H-1' of ITP and for H-8 and H-1' of GTP has been measured in D2O at 25 degrees C under several degrees of protonation in the pD range 1.2-8.4. For reasons of comparison, inosine and guanosine have been included in the study The results are consistent with the isodesmic model of indefinite noncooperative stacking. The association constants for the nucleosides (Ns) inosine and guanosine decrease with increasing protonation: Ns greater than D(Ns)+/Ns in a 1:1 ratio greater than D(Ns)+. In contrast, a maximum is observed with ITP and GTP; the stacking tendency of GTP following the series: GTP4- less than or equal to D(GTP)3- (K approximately 0.7 M-1) less than D(GTP)3-/D2(GTP)2- in a 1:1 ratio (K approximately 2.9 M-1) greater than D2(GTP)2- greater than D3(GTP)- (K approximately 1.5 M-1). The order of the series with ITP corresponds to that with GTP, but the association constants are slightly smaller. At the maximum of the self-association tendency the triphosphate residue has only a minor influence; this follows from the fact that the association constants for the 1:1 ratios of Ino/D(Ino)+ and D(ITP)3-/D2(ITP)2- are identical within experimental error; this holds also for Guo/D(Guo)+ and D(GTP)3-/D2(GTP)2-; in all these pairs the K-7 site is 50% protonated. Comparison of the association constant for the deprotonated species shows that here charge effects, i.e. repulsion between the negatively charged triphosphate chains, are important: Ino (K approximately 3.3 M-1) greater than ITP4- (K approximately 0.4 M-1) and Guo (K approximately 8 M-1) greater than GTP4- (K approximately 0.8 M-1). In addition the series holds: Ado (K approximately 15 M-1) greater than Guo greater than Ino. However, most important is the comparison of the ITP and GTP series with previous data for ATP: ATP4- (K approximately 1.3 M-1) less than D(ATP)3- (2.1 M-1) less than 1:1 ratio of D(ATP)3-/D2(ATP)2- (6 M-1) much less than D2(ATP)2- (approximately 200 M-1) much greater than D3(ATP)- (K less than or equal to 17 M-1).(ABSTRACT TRUNCATED AT 400 WORDS)     

Stimulation of cation transport in mitochondria by gramicidin and truncated derivatives

Gramicidin and the truncated derivatives desformylgramicidin (desfor) and des(formylvalyl)gramicidin (desval) stimulate monovalent cation transport in rat liver mitochondria. Cation fluxes were compared indirectly from the effect of cations on the membrane potential at steady state (state 4) or from the associated stimulation of electron transport. Rb+ transport was measured directly from the uptake of 86Rb. The truncated gramicidins show enhanced selectivity for K+ and Rb+ when compared to gramicidin. Moreover, the pattern of selectivity within the alkali cation series is altered, i.e., Rb+ greater than K+ greater than Cs+ greater than Na+ greater than Li+ for desfor and desval as compared to Cs+ greater than Rb+ greater than K+ = Na+ greater than Li+ for gramicidin. The cation fluxes through the truncated derivatives are more strongly dependent on the cation concentration. The presence of high concentrations of permeating cation enhances the transport of other cations through the truncated derivative channels, suggesting that cations are required for stabilizing the channel structure. In high concentrations of KCl, desfor and desval are nearly as effective as gramicidin in collapsing the mitochondrial membrane potential, and, consequently, in the uncoupling of oxidative phosphorylation and enhancement of ATP hydrolysis. Preliminary experiments with liposomes show that 86Rb exchange is stimulated by desfor and desval almost to the same extent as gramicidin. These results strongly suggest that the truncated gramicidins form a novel conducting channel which differs from the gramicidin head-to-head, single-stranded beta 6.3-helical dimer ("channel") in its conductance characteristic and its structure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Monovalent selectivity of the cyclic guanosine monophosphate-activated ion channel

Monovalent cation selectivity has been characterized for the 3',5'-cyclic guanosine monophosphate (cGMP)-activated channel in vertebrate photoreceptor outer segment plasma membranes without divalent cations. Macroscopic currents in excised, inside-out patches were activated with saturating concentrations of cGMP (200 microM). Using a bi-ionic protocol with symmetrical 120 mM ion concentrations across the membrane, alkali metal ions and certain organic cations were substituted for sodium on the cytoplasmic face. The relative permeabilities, determined from shifts in the reversal potential (Erev), were NH4 much greater than Na greater than guanidinium greater than K greater than Li greater than Rb greater than Cs (3.34: 1.0: 0.97: 0.93: 0.92: 0.74: 0.50, respectively). Erev's were also measured as a function of [Na], [NH4], and [Cs], and the slope of the relation was -59.8, -52.1, and -49.1 mV/decade, respectively. The slopes for NH4 and Cs differ significantly from the Nernst-Planck prediction of -58.2 mV/decade expected for a single ion channel. Relative permeabilities were also determined for the alkali metal series of ions with 20 mM ionic concentrations on both sides of the membrane. The permeability sequence at 20 mM was unchanged, but the relative permeability for NH4 and Cs deviated significantly from the measurements at 120 mM with 1.46 and 0.75 ratios, respectively. The dependence of Erev on absolute concentrations and the deviation from Nernst-Planck predictions are best explained by multi-ion occupancy of the cGMP-activated channel. Selectivity was also examined by comparing the conductance ratios as a function of potential.(ABSTRACT TRUNCATED AT 250 WORDS)     

An electronic mechanism in the actions of drugs and other cardinal adsorbents. I. Effects of ouabain on the relative affinities of the cell surface beta- and gamma-carboxyl groups for K+, Na+, glycine and other ions

The effects of ouabain on the effectiveness of glycine, Li+, Na+, K+, Rb+, and Cs+ in the external medium in reducing the rate of entry of labeled Cs+ into frog sartorius muscles were studied. The results showed that in the absence of ouabain the effectiveness of glycine and alkali-metal ions in inhibiting labeled Cs+ entry follows the rank order: K+ greater than Cs+, Rb+ greater than Na+, Li+ greater than glycine. Exposure to ouabain in essence reverses this order which then becomes: glycine greater than Li+, Na+ greater than K+, Rb+, greater than Cs+. These results confirm the prediction of the basic electronic interpretation of drug action according to the association-induction hypothesis. In addition, it shows that the action of ouabain on the surface beta- and gamma-carboxyl groups of frog muscle mediating Cs+ entry is quite similar to its action on the cytoplasmic beta- and gamma-carboxyl groups that are the seats of K+ accumulation in the bulk phase cytoplasm as well as to its action on the cell surface beta- and gamma-carboxyl groups responsible for the generation of the resting potential. In all these cases, ouabain acts as an electron-donating cardinal adsorbent (EDC). Finally the marked increase of the binding strength of glycine on the surface beta- and gamma-carboxyl groups was used to explain the primary pharmacodynamic effect of cardiac glycosides in combating heart failure.     

Complexation studies on inositol-phosphates. II. Alkali-metal complexes of D-myo-inositol 1,2,6 trisphosphate

The complexation properties of the D-myo-inositol 1,2,6 trisphosphate (Ins(1,2,6)P3) towards Li+, Na+, K+, Rb+, and Cs+ cations were studied at 25 degrees C in a 0.1 M tetra-n-butylammonium bromide medium. For all cations, mononuclear and protonated species were found. For smaller cations (Li+, Na+, and K+) a dinuclear complex was also put into evidence. The main characteristic of the complexes is its high stability; and of the ligand, its nonselectivity. The Ins(1,2,6)P3-K system was ascertained using Sammartano's method which additionally enabled the influence of various K+ concentrations on the protonations constants to be considered.