Bruce Enos | University of California, Los Angeles (original) (raw)

Papers by Bruce Enos

Journal of Theoretical Biology, 1981

In this paper we calculate the hydrogen ion titration curves and associated surface potential for... more In this paper we calculate the hydrogen ion titration curves and associated surface potential for a lattice of discrete sites by numerically solving a titration equation constructed by expanding the partition function for the lattice in powers of the density of charged groups. The titration equations were calculated for several different lattice spacings and ionic strengths of the bathing solution. The results of applying this theory to several simple models of the membrane-solution interface is compared to the corresponding results obtained via the uniform-charge model. 499

Biochimica Et Biophysica Acta-biomembranes, 1981

The zero-current membrane potential and the current-voltage relations are discussed theoretically... more The zero-current membrane potential and the current-voltage relations are discussed theoretically for the case in which ionic transport is mediated by carriers that form complexes with ions in the aqueous phase ('solution complexation' mechanism). Interest for this topic originated partly from the finding that gradients of the neutral cyclic peptide PV, cyelo (DVaI-LPro-LVal-I)Pro)3, commonly thought to act as a carrier via 'solution complexation', generate Nernstian potentials across lipid bilayers separating solutions of identical ion composition. It is shown that the general expression for the potential in ~i gradient of carriers reduces to the Nernst equation under any of the following conditions: slow aqueous reaction; impermeability of the membrane to the neutral carriers; high concentration of the complexing ions m solution; finite permeability of the membrane to the neutral carrier, but faster rate of movement from the membrane surface into the torus than across the middle or out of the membrane. In symmetrical solutions, the conductance is most typically characterized by a quantity that we designate by 8", which has the dimensions of a length and is generally a complex function of ion activity. Comparing the thory with previous data on dioleoylphosphatidylcholine membranes in the presence of PV and K ÷, the order of magnitude of the rates of the aqueous reaction and of the membrane permeability to the neutral carriers is tentatively estimated. 0005-2736/81/0000-0000/$02.50

Upsala Journal of Medical Sciences, 1980

The conductance-voltage (G-V) characteristic of a single-filing, multi-barrier, multi-occupancy c... more The conductance-voltage (G-V) characteristic of a single-filing, multi-barrier, multi-occupancy channel depends in the limit of low ion concentration upon only two parameters: the voltage dependence of the entry step and the ratio of the rate constant for leaving the channel to that for crossing its middle (14,17,20). We show that the G-V shape in this low concentration limit can be measured accurately using a triangular wave, many-channel technique and demonstrate that the observed shape is incompatible with that expected if the only important rate limiting barrier at low concentration were at the channel mouth. Instead the central barrier turns out, surprisingly, in view of the markedly sublinear I-V shape at low concentration, to be even slightly larger than the exit barrier. Additionally, we find that it is not possible to fit both the G-V shape and the concentration dependence of the zero-current conductance simultaneously with a 3-barrier 2-site model. However, by adding additional sites to yield a 3-barrier 4-site model either of the type 3B4S" where the extra site in each channel half is external to the mouth of the channel or of the type 3B4S' where the extra site is internal to the mouth of the channel, we obtain good agreement. Additionally, using the flux ratio data of Procopio and Andersen (19) to discriminate between 3B4S and 3B4S" models, we find the 3B4S" model to be the only satisfactory one.

Annals of The New York Academy of Sciences, 1980

The cationic channel formed by the uncharged polypeptide backbone of the gramicidin A dimer is a ... more The cationic channel formed by the uncharged polypeptide backbone of the gramicidin A dimer is a simple and well characterizable prototype for the less easily studied types of ion-selective channels of the cell membrane. Excitable membranes are known to contain several types of ionic channels, each of which has come to be recogmzed' to be a macromolecular pore capable of passing millions of ions per second and yet narrow enough to exhibit some selectivity as to the charge and size of the ions allowed to pass as well as to show signs of "singlefiling*'.'-3 A number of important conceptions about the general properties of channels have been confirmed by experimental findings in gramicidin A and by the theory that is developing to account for For example, recent findings on gramicidin channels indicate that such channels are able to contain several interacting permeant ions simultaneo~sly'*'~.~ and are also SQ narrow that ions and water molecules are not permitted to pass each other?t.28*29 This supports the current view as to the likelihood of such behavior in the Na+ and K+ channels of The findings, in roughly chronological sequence, for excitable membranes and for gramicidin, are: single-filing flux coupling,20*2t concentrationdependent permeability ratio^.^-^^ block in mixture of cations'. '% and coupling between ion-flux and water flu^.^*^ The conductanceconcentration behavior for the gramicidin channel in single salts also indicates the existence of at least two classes of sites with different binding constants for the group la cations: t % Here we will provide further evidence for multiple occupancy from the changes in shape that occur in the current-voltage relationshp of single gramicidin channels when the ionic concentration is changed. Finally, although the highly selective H+ permeation of the gramicidin channel has long been k n~w n : *~*~ new, and surprising, data on the H+ permeation properties of the gramicidin channel, which we will present here, indicate that this channel may provide a much more %* n. m and three classes for TI4* ''* and Ag3'

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Epilepsia, 2003

Summary: Purpose: To examine evidence for effectiveness of anteromesial temporal lobe and localiz... more Summary: Purpose: To examine evidence for effectiveness of anteromesial temporal lobe and localized neocortical resections for disabling complex partial seizures.Methods: Systemic review and analysis of the literature since 1990.Results: One intention-to-treat Class I randomized controlled trial of surgery for mesial temporal lobe epilepsy found that 58% of patients randomized to be evaluated for surgical therapy (64% of those who received surgery) were free of disabling seizures and 10 to 15% were unimproved at the end of 1 year, compared with 8% free of disabling seizures in the group randomized to continued medical therapy. There was a significant improvement in quantitative quality-of-life scores and a trend toward better social function at the end of 1 year for patients in the surgical group, no surgical mortality, and infrequent morbidity. Twenty-four Class IV series of temporal lobe resections yielded essentially identical results. There are similar Class IV results for localized neocortical resections; no Class I or II studies are available.Conclusions: A single Class I study and 24 Class IV studies indicate that the benefits of anteromesial temporal lobe resection for disabling complex partial seizures is greater than continued treatment with antiepileptic drugs, and the risks are at least comparable. For patients who are compromised by such seizures, referral to an epilepsy surgery center should be strongly considered. Further studies are needed to determine if neocortical seizures benefit from surgery, and whether early surgical intervention should be the treatment of choice for certain surgically remediable epileptic syndromes.