Platelet tagging with tritium labeled diisopropylfluorophosphate.

By EDWARD ADELSON, RICHARD M. KAUFMAN, Cmo BERDEGUEZ, ARNOLD A. LEAR AND JACK J. RHEINGOLD F OR THE PAST 10 years, P32 labeled diisopropylfluorophosphate has been used to tag platelets.”2 This compound attaches to various proteins, during which process it changes from diisopropylfiuorophosphate ( DFP) to diisopropylphosphate (DIP).3 The DIP is irreversibly bound to the protein molecule until that molecule breaks down and then the DIP is not reutilized.5 Although its major attachment has generally been considered to be to the cholinesterase molecule, DFP will attach to any protein that has a serine group.4 Its major pharmacologic action depends on its combining with cholinesterase and inhibiting the action of that compound, resulting in symptoms associated with overactivity of the parasympathetic nervous system.#{176} Usually doses of up to 3 milligrams of DFP in humans will produce little or no side effects. However, when the dose of DFP reaches 4 milligrams, side effects are often seen.4 P32 labeled diisopropylfluorophosphate has the drawback of a relatively low specific activity since there is only one atom of phosphorus in the molecule. The short half-life of p32 results in a short shelf-life for the compound, further reducing the specific activity toward the end of the usual 10-day to 2-week survival studies. The specific activity of the tag cannot be increased by increasing the dose of DFP, because of the pharmacologic toxicity of the compound. Furthermore, increasing the dose of DFP gives diminishing results, as will be shown in the in vitro studies reported here. This low specific activity has resulted in some difference of opinion as to whether the survival curves of platelets labeled with DFP32 are linear or exponential. Leeksma and Cohen,’ Alfos et al.,7 Zucker et al.,8 and others