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M O Young

Publications and source records attributed to M O Young.

4 recordsLinked to original sources
PubMed1989

Heterogeneity of membrane transport quantified by the analysis of a unidirectional flux transient of charged tracer.

A planar mosaic membrane consists of patches, each with a given area, diffusion coefficient, and mobility of charged tracer; a common electric field, constant in space and time, lies across all the patches. Given the properties of the patches, the transient of the total unidirectional flux (summed over the patches) is predictable. Here we deal with the inverse problem: Given only the observed transient of the total unidirectional flux (as defined experimentally by Ussing), the unknown transport heterogeneity of the mosaic membrane is to be analyzed. Results obtained previously for uncharged tracers are generalized to include effects of the field. In particular, the ratio of the arithmetic and harmonic means (both area-weighted) of the diffusion coefficients, evaluated over the membrane, is expressed in terms of only the observed transient and the field strength and is used to characterize the heterogeneity; and the unique exact solution of the inverse problem for two kinds of patches is recovered at any field strength. If the mosaic consists of n distinct kinds of patches, a sweep of the field strength from low to high values reveals (at most) n steplike shapes in the time course of the total unidirectional flux (normalized to its final steady value), which permit an approximate analysis of the heterogeneity by elementary means.

Biological Transport, Active↗
PubMed1987

Metabolites of 2-deoxyglucose in rat brain at 12-24 h: bounds on kinetic constants.

Activities of 2-deoxy-D-glucose and its metabolites in rat brain were examined at 12, 16, 20, and 24 h after intraperitoneal injection of 14C-labeled 2-deoxy-D-glucose. Plasma radioactivity was monitored for 2 h before each of these determinations. As proportion of total brain radioactivity, 2-deoxy-D-glucose decreased monotonically from the unexpectedly high value of 22% at 12 h to 11% at 24 h after injection, 2-deoxy-D-glucose 6-phosphate decreased monotonically from 69% at 12 h to 23% at 24 h, and unphosphorylated products (of high and low molecular weight) increased from 10% at 12 h to 64% at 24 h. The data were analyzed in terms of a four-compartment model. Secure lower and upper bounds on the rate constant, k4*, for the dephosphorylation of 2-deoxy-D-glucose 6-phosphate were established: k4* was at least 0.0158 +/- 0.0014 . min-1 and at most 0.0385 +/- 0.0037 . min-1. If k4* is constant in time, then appreciable dephosphorylation occurs within the 45-min experimental period commonly used in the standard 2-deoxy-D-glucose method for estimating local cerebral glucose utilization. The possibility that the effective k4* is lower at such early times is reviewed in the light of a reanalysis of previously published data. Implications of these results for the 2-deoxy-D-glucose method are discussed from the points of view of numerical analysis and capillary heterogeneity.

Animals↗