Effect of temperature on hydraulic conductivity of single capillaries

Paired determinations of the hydraulic conductivity (Lp) of individually perfused capillaries in frog mesentery were measured at 22-25 and 5-8°C. The mean value of the ratio of the hydraulic conductivity at 22-25 to that at 5-8°C was 1.76±0.22 (SE) in 10 capillaries perfused with albumin in the Ringer perfusate and 1.81±0.11 in six capillaries perfused with Ringer alone. The ratio of Lp can be accounted for in terms of a 1.60-fold increase in water viscosity between 22-25 and 5-8°C. The results conform to the hypothesis that capillary wall is invariant with temperature; models of the water pathway that imply a change in the number of pathways or a change in pathway structure with temperature are incompatible with these results. Temperature gradients across the tissue are negligible in these experiments; calculations show that in the presence of temperature gradients, which occur during tissue cooling or rewarming, transcapillary water flows due to thermoosmosis are likely to occur.