PubMed · 10257524
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
L Champlin. 1982. Understanding TENS purchasing.. https://pubmed.ncbi.nlm.nih.gov/10257524/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
An experimental protocol, using an initial 1 min direct current (DC) applied potential of 4 V followed by alternating current (AC), was established to: (a) increase conductance and permeability and decrease lag time for human epidermal membrane (HEM) relative to unaltered HEM and; (b) maintain constant conductance and permeability during flux studies. The protocol allowed specific permeation parameters of the membrane to be characterized under electrically enhanced, constant flux conditions. The permeability, lag time, and effective membrane thickness were determined using a nonionic polar permeant, urea, while the enhanced conductance was maintained at a constant level with AC. A tortuous pore pathway model was employed to analyze the data. The AC protocol increased membrane permeability, and decreased lag time and effective membrane thickness relative to similar parameters obtained in previous studies from unaltered HEM. Lag times ranged from 32.0 to 105.5 min, and permeability coefficients calculated from steady state fluxes ranged from 1.68 to 6.03x10(-7) cm/s for HEM samples with electrical resistance values during transport of 2.3-8.0 kOmega x cm2. Effective membrane thicknesses were calculated to range from 0.34 to 0.61 cm during AC iontophoresis. Significant additional results were obtained when the protocol was applied for two consecutive runs using the same HEM sample, with time for the HEM sample to recover between runs. During the second run, the applied potential was adjusted to reproduce the conductance obtained on the first run. Under these conditions, the consecutive runs yielded essentially the same lag time, permeability and effective membrane thickness values. These results suggest that constant fluxes can be achieved by keeping HEM electrical conductance constant during AC iontophoresis.
The photosynthetic reaction center is one of the most complicated molecular complexes. Transducing photon energy to a transmembrane electrochemical potential difference for protons, it is the direct or indirect energy source for virtually all life. We show here that it operates in a simple, battery-like manner, with a maximum potential of 0.20 V. Intriguingly this is only one fifth of the energy of the absorbed photon.
Electrical stimulation of human upper limb muscle tendons produces a reflex inhibition (I(1)) in the same muscles. This inhibition is reduced in Parkinson's disease (PD), prompting a similar study of essential tremor (ET). In essential tremor, two of eight subjects had no discernible inhibition, even following supramaximal stimulation (< 80 mA) of the tendons from extensor digitorum communis and extensor pollicis brevis. In the remaining six subjects, the mean thresholds for I(1) in these muscles were increased by 270 and 320%, respectively, relative to controls. The maximal amplitude of the inhibition was significantly reduced in the ET group, as was the following excitation (E(1)). The latency and duration of I(1) were not different in ET subjects and controls. The maximal duration of I(1) was correlated with tremor frequency in individuals, and tendon stimulation was effective in initiating ongoing tremor cycles. These results disclose a peripheral reflex abnormality in ET that is mediated by tendon afferents and can be linked to the coexistent tremor. The response in ET was distinguished from that in PD by its different time-course and by failure of the response to appear in the antagonist muscle. The abnormality may prove a useful marker for ET, which currently lacks a definitive pathological or neurophysiological marker to support objective clinical diagnosis.