Manuel Schwartz

Structural dependence of electrical conductivity of thin tellurium films

Tellurium films were deposited on glass substrates and maintained in vacuum during the course of the measurement of electrical conductivity. The films were found by electron microscopy to have polycrystalline structure with a grain size dependent on deposition parameters. The electrical conductivity increased with increasing thickness, with increasing rate of deposition, and with the transition from the nonannealed to the annealed state. The increase in deposition rate from 100 to 1000 A/min led to an increase in both grain size and number of surface defects. Annealing resulted in a further increase in grain size but in a decrease in the number of defects. The conductivity could further be explained in terms of mobility and carrier concentration, the former increasing with increasing grain size and decreasing defects, and the latter increasing with increasing defects. A comparison of quenched and annealed films confirms the dependence of mobility on the number of defects.

Anomalous potential response and (Na+ + K+)-ATPase in in vitro frog gastric mucosa

In general, increasing K+ on the nutrient side decreases the transmucosal PD (nutrient becomes more negative) but after bathing the mucosa in zero K+ media for about 30 min, or longer, elevation of K+ on the nutrient side increases the PD, an anomalous effect. In Cl- media, increasing nutrient K+ from zero to 4 mM produces an increase in PD (an anomalous response) of 3.1 and 5.3 mV in 2 and 5 min, respectively. Ouabain (10(-3) M) to the nutrient side abolished the anomalous response as did removal of Na+ (choline for Na+) from bathing media. In SO4(2-) media (SO4(2-) for Cl-), a significant anomalous PD response was observed when K+ on the nutrient side was increased from zero to 1, 2 or 3 mM but not to higher K+ concentrations. In this case, ouabain also abolished the anomalous response. It is postulated, on the basis of the effects of ouabain and the use of choline media, that an electrogenic (Na+ + K+)-ATPase pump is present on the nutrient-facing membrane in which more Na+ than K+ are transported per cycle.

Evidence for HCO3− conductance pathways in nutrient membrane of resting frog fundus

Abstract The effect on potential difference (PD) and resistance in Cl − media bathing the resting fundus of Rana pipiens was determined for nutrient HCO 3 − changes from 25 mM to several lower concentrations and back to 25 mM. The graph of |vbΔPD|vb versus log[HCO 3 − ] was linear for changes from 25 down to 3.1 mM and also back to 25 mM, but deviated considerably for changes to 1.6 mM. The fact that changes from higher to lower HCO 3 − gave a less rapid initial PD response than the reverse direction eliminated H + conductance pathways as being predominant. Experiments were done in which in the first part changes were made in the nutrient solution from 5% CO 2 and 25 mM HCO 3 − to 0.6% CO 2 and 3 mM HCO 3 − and in the second part, the same changes with the simultaneous change of secretory solution from 5% to 10% CO 2 . The magnitude of the PD decrease was greater by 4.0 mV in the second part. This result indicated that HCO 3 − rather than OH − conductance pathways predominated. On the secretory side, the change from 25 to 3.1 mM HCO 3 − gave a small but significant change in PD. The latter effect was too small to determine whether HCO 3 − pathways existed in the secretory membrane.

Electric Impedance and Rectification of Fused Anion-Cation Membranes in Solution

At relatively high currents, fused anion-cation membranes give rise to rectifying and reactive effects. The rectification becomes less pronounced with increasing frequency. This effect results from changes in the concentration profiles of the ions during the positive and negative phases of the AC cycle. With reduction of the current, the voltage-current response becomes linear. The reactive effect can then be separated from the rectifying effect. The former effect can be attributed essentially to two factors: (a) the presence of transition regions of fixed charge and (b) the diffusion mechanism of the ions in an AC field. The first factor is largely frequency-independent and the second, frequency-dependent. A first approximation equivalent circuit is described. This circuit involves frequency-dependent elements.

Potential difference responses due to K+, Na+ and Cl− changes in Bullfrog antrum with and without HCO3−

The effect of changing [K+], [Na+] and [Cl-] in nutrient solution was studied in bullfrog antrum with and without HCO3- in nutrient. In 25 mM HCO3- (95% O2/5% CO2) and in zero HCO3- (100% O2), nutrient pH was maintained at 7.3. Changing from 4 to 40 mM K+ or from 81 to 8.1 mM Cl- gave a decrease 10 min later in transmucosal PD (nutrient became more negative)--a normal response. These responses were less in zero than in 25 mM HCO3-. A decrease from 102 to 8 mM Na+ decreased PD (anomalous response of electrogenic NaCl symport). This effect was attenuated or eliminated in zero HCO3-. In contrast, change from 4 to 40 mM K+ gave initial anomalous PD response and change from 102 to 8 mM Na+, initial normal PD response with either zero or 25 mM HCO3-. Both responses were associated with (Na+ + K+)-ATPase pump and were greater in zero than in 25 mM HCO3-. Initial PD increases in zero HCO3- are explained as due to increase in the resistance of passive conductance and/or NaCl symport pathways. Thus, removal of HCO3- modifies conductance pathways of nutrient membrane.

A Confirmation of Electrogenicity of Frog Gastric Mucosa by Using Methoxyflurane

Conclusion Methoxyflurane, like dinitrophenol, acts only on the H+ secretory mechanism in Cl--free solutions. This anesthetic also reveals the linear relationship between the PD and H+ rate and permits estimates of the parameters of the H+ secretory mechanism in Cl--free solutions.

Effects of Barium on the in Vitro Frog Gastric Mucosa

Conclusion The addition of Ba++ to the fluid bathing the nutrient side of the frog gastric mucosa resulted in a marked increase in resistance and relatively little change in the H+ rate and the PD. Addition of Ba++ in comparable and higher concentrations to the secretory fluid had no effect.

Effect of melittin on PD, resistance and short-circuit current in the frog gastric mucosa.

In an in-vitro preparation of gastric mucosae of Rana pipiens, the effect of adding melittin to a concentration of 5x10-6 M in the secretory solution on the transepithelial potential difference (PD), resistance (R) and short-circuit current (Isc) was studied. In 20 min, melittin decreased the PD by 9.3 mV and R by 148 ohm cm2. These changes can be explained by a decrease in the resistance, RP, of the paracellular pathway. To determine whether specific-ion pathways were responsible for the decrease in R, the effect of melittin on the partial conductances of Cl-, K+ and Na+ was also studied using the ion substitution method. Melittin decreased the PD response to changes in nutrient Na+, K+ and Cl- and the PD response to changes in secretory Cl-, but did not affect PD responses to changes in secretory Na+ or K+. Therefore, melittin decreased the nutrient membrane partial conductances of Cl-, K+ and Na+ and secretory membrane partial conductance of Cl-, without affecting the secretory partial conductances of Na+ or K+. Initially, melittin increased Isc in regular and Cl--free but not in Na+-free solutions. There was a delayed decrease in Isc. The results indicate that melittin decreases RP, increases the Na+ conductance of the secretory membrane and inhibits, eventually, the Na+/K+-ATPase pump.

Amphotericin B enhanced anomalous potential difference response to changes in aqueous K+ in frog cornea

An increase in aqueous K+ from 0 to 4 mM increased the potential difference (anomalous response of electrogenic (Na+ + K+)-ATPase antiport) by 1.1 mV in Cl(-)-free solutions compared to 6.8 mV in Cl- solutions. With amphotericin B added to the tear solution in Cl(-)-free solutions, the anomalous PD response for the addition of 4 mM K+ to the aqueous solution was about 20 mV, significantly greater than in Cl- solutions. This anomalous response was inhibited by ouabain. These data support the electrogenicity of the (Na+ + K+)-ATPase pump. It is also evident that, for the pump to respond, Na+ should readily enter the cell. This may be accomplished experimentally, either across the basolateral membrane in Cl- solutions or across the apical membrane in Cl(-)-free solutions with amphotericin B present in the tear solution.

Effects of ouabain on frog gastric mucosa in vitro

The effect of the addition of ouabain to the nutrient solution was determined on resistance, potential difference (p.d.) and H+ secretion rate. In NaCl media, 10(-3) M ouabain decreased significantly the p.d. from 25.6 mV to 16.1 mV in 30 min and to 11.0 mV in 60 min. No significant changes occurred in resistance and H+ secretion rate. In Na2SO4 (Cl(-)-free) media, ouabain produced a biphasic effect on p.d. The p.d. changed from -28.0 mV (nutrient-negative) to a nadir of -37.4 mV in 7 min and then increased to -16.4 mV in 60 min. At the nadir there was no significant change in resistance or H+ secretion rate but at 60 min, unlike Cl- media, resistance increased by 36% and H+ secretion rate decreased by 43%. To decide whether the ouabain-caused decrease in H+ rate in Na2SO4 media was due to an effect on the H+ pump or on resistance of the return pathways, the voltage was clamped at 0 and 40 mV. Clamping the voltage showed that in the case of a marked decrease in the H+ secretion rate, the H+ transport mechanism itself was inhibited (and not the parallel pathway). The decrease in p.d. due to ouabain in Cl- and SO42- media indicates that the (Na+ + K+)-ATPase mechanism may be electrogenic.