An analysis of the D-glucose influx kinetics of in vitro hamster jejunum, based on considerations of the mass-transfer coefficient.

1. A study designed specifically to investigate the effects of unstirred layers on the apparent glucose-influx kinetics of hamster jejunum was conducted. 2. The apparent V was 12.81, 10.71, 9.75, 10.17 and 9.33 mumol/cm-2 - h while the apparent Km was 7.42, 3.95, 1.87, 0.93 and 0.5 mM, respectively, when the rate of shaking the incubation flasks was 40, 80, 120, 160 and 200 cycles/min. 3. Extrapolation of the slope and reciprocal intercept of Lineweaver-Burke plots of the data to infinite shaking rate is mathematically justified to yield the slope and intercept of a Lineweaver-Burk plot which is uncomplicated by unstirred layers. These extrapolations were found to have a regression coefficient = 1 when plotted as (intercept)-1 or slope = b0 + b1b-(shake)-2 where b = 2.764 for the slope plot and 6.626 for the (intercept)-1 plot. From the values of b0 one obtains a Km of 0.41 and a V 0f 0.35 which should represent the true kinetic parameters for glucose influx into this tissue under the experimental conditions employed. 4. Values of the theoretical flux expected on a basis of unstirred-layer thickness which was calculated from the relation Cb (for J = V/2) = Km + 0.5 V/Kd agreed with the experimental values of J in some instances but the 95% confidence interval of the theoretical and experimental values did not overlap in many instances at low shaking rates and low concentrations of glucose. 5. A factor theta representing the error between the theoretical and experimental values was found to fit the relationship 1n(theoretical J) = - 3.8 + 5.77 (1/theta) with a regression coefficient of 0.98 and was proposed to be due to one or more of the following parameters: (1) a villus tip to base gradient of transport (influx) activity; (2) a dependence of brush-border influx area on substrate concentration in the bulk incubation media; and (3) an end-product inhibition of the overall transport rate. 6. It is apparent from the data that the flux of glucose across the unstirred layer is ordinarily the rate-limiting step in the trans-brush-border transport of this sugar by hamster jejunum when less than saturating concentrations of glucose are used. At high shaking rates the contribution of the unstirred layer is reduced.