Thiopental binding to human serum albumin in the presence of halothane

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Abstract
In vitrothiopental binding (substrate concentration 0.04 · 10‐3M=10 μg/ml) to 1% human serum albumin (HSA)increasedsignificantly from 40.2% (=control) to 47.3% in the presence of 1.18 · 10‐3M = 2.84 vol% halothane. A 4‐fold higher halothane concentration (4.71 · 10‐3M) had an even greater effect with anincreasein the thiopental fraction bound to 55.5%. With a constant HSA concentration (1% or 5%) and thiopental concentrations in the range 0.01–1.5 · 10‐3M or 0.01–0.38 · 10‐3M, respectively, the halothane effect (increasein thiopental binding) was always evident, as well as in other experiments with constant thiopental concentration (0.04 · 10‐3M) and variation in the HSA concentration (0.5 – 10%). Two classes of binding sites for thiopental were apparent at the HSA molecule. In the control experiments the following binding parameters were found: n1=0.01, k1= 181 · 103M‐1; n2=45.73, k2=0.08 · 103M‐1, K=5.47 · 103M‐1. In the presence of halothane the binding parameters changed as follows: n1= 0.14, k1=29.4 · 103M‐1; n2= 11.68, k2=0.42 · 103M‐1, K=9.02 · 103M‐1