Normal values and membrane markers of theophylline-sensitive and theophylline-resistant human T-lymphocytes.

In 32 healthy adults between 20 and 50 years, the number of theophylline-resistant T-lymphocytes (T-res) was determined to be 51 +/- 4% or 1,161 +/- 326 per microliter, and that of theophylline-sensitive T-lymphocytes (T-sens), 11 +/- 2% or 252 +/- 95.--The decrease in number of rosette-forming cells after incubation with 1 mM theophylline was not caused by reduced vitality (51Cr-release test). The testing of various theophylline concentrations (1, 3, 5, and 10 mM) did not result in a changed count of T-sens. By a variation of the lymphocyte: sheep erythrocyte ratio and of incubation temperature it was found that T-sens possess high-affine and T-res low-affine receptors for sheep erythrocytes. While about 30% of the cells of both subpopulations proved to have Fc-IgM-receptors, among T-sens a significantly higher number of cells carried Fc-IgG-receptors than among T-res (29% vs. 10%).

Is adenosine an endogenous anticonvulsant?

The anticonvulsant properties of adenosine were tested pharmacologically on amygdala-kindled seizure activity in rats. The adenosine analogue 2-chloroadenosine and the adenosine uptake blocker papaverine both increased the latency to behavioral clonus as well as reduced the duration and severity of the clonic motor convulsion. Both drugs, however, failed to alter the postkindling afterdischarge (AD) threshold. Theophylline, an adenosine antagonist, had the opposite effects, prolonging the AD and motor seizure durations and facilitating partially kindled seizures, but again not altering the prekindling or postkindling AD thresholds of amygdala-elicited seizures. In contrast, carbamazepine raised AD thresholds, suggesting that it does not produce its anticonvulsant effects through adenosine systems. Since endogenous adenosine can impede seizure spread and seizure continuation, but does not affect seizure initiation from the amygdala, perhaps endogenous adenosine has the special property of being brought into play as an anticonvulsant only by the seizure itself.