Biomedical subjects

D W Tank

Publications and source records attributed to D W Tank.

58 records · Page 4Linked to original sources

PubMed1982

Isolated-patch recording from liposomes containing functionally reconstituted chloride channels from Torpedo electroplax.

Small unilamellar vesicles formed from purified phospholids by detergent/dialysis methods may be enlarged to 30-microns diameter by freezing and thawing. Very-high-resistance seals were formed by applying a glass micropipette to the surface of these large liposomes, and single bilayer "patches" of membrane were isolated from the liposome surface while remaining sealed to the micropipette. The exogenous channel-forming peptides gramicidin and alamethicin induced characteristic single-channel fluctuation behavior in these excised patches held under voltage-clamp conditions. Large liposomes were formed from the small unilamellar vesicles made from cholate extracts of Torpedo electroplax plasma membrane vesicles. Isolated patches formed from these reconstituted membranes displayed current fluctuations due to single voltage-gated Cl- channels from non-innervated-face membranes; the properties of these Cl- channels are identical to those observed in planar bilayer membranes after direct insertion from native membranes. This liposome-patch method combines the advantages of membrane protein incorporation into liposomes with high-resolution electrical recording methods and may provide a generally applicable approach to the study of integral membrane channel proteins after solubilization and reconstitution.

Animals↗

PubMed1982

Enhanced molecular diffusibility in muscle membrane blebs: release of lateral constraints.

Measurements of lateral molecular diffusion on blebs formed on the surfaces of isolated muscle cells and myoblasts are reported. These blebbed membranes retain integral proteins but apparently separate from the detectable cytoskeleton. On blebs, acetylcholine receptors, concanavalin A receptors, and stearoyldextran extrinsic model receptor molecules are free to diffuse with a diffusion coefficient (D) approximately 3 x 10(-9) cm2/s, which is close to the value predicted for hydrodynamic drag in the lipid membrane. In contrast, diffusion of these typical receptors in intact cell membranes is constrained to D approximately less than 10(-10) cm2/s with substantial fractions virtually nondiffusible (D less than 10(-12) cm2/s). Lipid analog diffusion is also slightly enhanced in blebs as expected of evanescent lipid protein interaction. This strong enhancement of membrane protein diffusion is attributed to release from unidentified natural constraints that is induced in some way by detachment of the bleb membrane.

Animals↗

PubMed1981

Molecular mobility on the cell surface.

Many measurements of lateral diffusion of proteins and lipids on cell membranes and lipid model membranes have become available through application of fluorescence photobleaching recovery methods. A puzzling aspect of these results is slow diffusion and partial immobilization of protein molecules on the cell surface. Observed protein diffusion coefficients on vertebrate structural tissue cells are consistently D less than or equal to 10(-10) cm2/s, while lipid analogues diffuse with D approx. 10(-8) cm2/s. Substantial fractions of the cell membrane proteins are not diffusible. In a pure viscous membrane, theoretical fluid dynamics has suggested only small differences between lipid and protein diffusion coefficients. Measurements of protein diffusion in model membranes recently showed D less than or equal to 10(-9) cm2/s, as expected. Recent experiments on cell membranes show that uncoupling of the membrane from the cytoskeleton by formation of blebs releases the membrane protein molecules so that diffusion is enhanced to D greater than or equal to 10(-9) cm2/s and the non-diffusible fraction is eliminated.

Actins↗

PubMedDate not supplied

The autapse: a simple illustration of short-term analog memory storage by tuned synaptic feedback.

According to a popular hypothesis, short-term memories are stored as persistent neural activity maintained by synaptic feedback loops. This hypothesis has been formulated mathematically in a number of recurrent network models. Here we study an abstraction of these models, a single neuron with a synapse onto itself, or autapse. This abstraction cannot simulate the way in which persistent activity patterns are distributed over neural populations in the brain. However, with proper tuning of parameters, it does reproduce the continuously graded, or analog, nature of many examples of persistent activity. The conditions for tuning are derived for the dynamics of a conductance-based model neuron with a slow excitatory autapse. The derivation uses the method of averaging to approximate the spiking model with a nonspiking, reduced model. Short-term analog memory storage is possible if the reduced model is approximately linear and if its feedforward bias and autapse strength are precisely tuned.

Action Potentials↗