Low Electric Potential Research Articles

ATP synthesis by ATPase proteoliposomes from the thermophilic cyanobacterium Synechococcus 6716 by ionophore-induced electric potentials and proton gradients

ATP synthesis driven by low pre-established electric potentials and pH gradients is studied in large ATPase proteoliposomes, prepared from the ATPase complex and native lipids from the thermophilic cyanobacterium Synechococcus 6716. Electric potentials and pH gradients were achieved by valinomycin and nigericin, respectively, in the presence of a K + gradient across the membrane. External base-pulses were also applied. In this system ATP synthesis driven by valinomycin-induced K + influx, nigericin-induced internal acidification and by external base-pulses is demonstrated. Electric potentials and pH gradients of equivalent size lead to roughly similar ATP synthesis activities. ATP synthesis is optimal at 80–100 nM valinomycin and at 0.75−1 μM nigericin at the proper pre-set ion gradients. Uncoupler and DCCD inhibit ATP synthesis. Prior activation of the complex by thiol agents or trypsin was not required for synthesis activity. The ATP synthesis rate increases with the size of electric potential or pH gradient. The threshold value of the electrochemical gradient for significant ATP synthesis is about 30 mV. ATP production proceeds for more than 60 min. The generation of ionophore-induced electric potentials and pH gradients have been followed by oxonol VI and intraliposomal Neutral red, respectively. The extent of the absorbance changes of both probes is proportional to the size of electric potential or pH gradient. Ionophore-induced oxonol VI and Neutral red responses are stable for at least 30 min. The results are discussed in terms of membrane permeability and vesicle size.

Visual, Brainstem Auditory and Somatosensory Evoked Potentials: Clinical Uses

ABSTRACT.Visual, brainstem and somatosensory evoked potentials have added new dimensions to electrophysiological studies. Signal averaging has made it possible to record low amplitude electrical potentials in the nervous system to external stimuli. Clinical abnormalities are indicated by latency prolongations, furnishing objective evidence for suspected or subclinical disease.The tests are most extensively used for diagnosis of multiple sclerosis (MS). Other indications include hearing and visual evaluation especially in neonates, diagnosis of brainstem and cerebellopontine angle tumors, monitoring the integrity of sensory function during scoliosis or neurosurgical procedures and differentiating toxic or metabolic causes of coma from irreversible structural lesions.The tests are noninvasive and considered in conjunction with the clinical data, provide useful electrodiagnostic tools.

Electrostatic disjoining pressure in symmetrical films with adsorptive charge regulation

The case of a film containing k strong 1:1 electrolytes sandwiched between nonpolar phases is considered at low electric surface potentials. An analytical equation for the electrostatic disjoining pressure under adsorptive charge regulation is obtained. It gives the well-known limiting cases of constant surface charge or potential depending on the value of a dimensionless parameter Φ. The calculated balance between van der Waals' attraction and electrostatic repulsion is in agreement with experimental evidence for the dependence on electrolyte concentration of the transition between common black and Newton water foam films stabilized with nonionic surfactants.