EFFECTS OF ALPHA-TRINOSITOL ADMINISTERED EXTRACELLULARLY AND INTRACELLULARLY (USING LIPOSOMES) ON RAT AORTA RINGS

The effects of alpha-trinositol, a D-myo-inositol [1,2,6]trisphosphate derivative, were studied on de-endothelised rat aorta rings. The subs tance was applied extracellularly as well as intracellularly (by using liposomes as drug carriers). Upon extracellular administration, the d rug reduced the level of contraction induced by 40 mM K+ or by phenyle phrine (10(-5) M). No effects were observed on relaxed preparations. L iposomes containing alpha-trinositol induced a dose-dependent contract ion of the preparations under resting tension with a threshold of 10(- 5) M in the aqueous phase. These contractions were heparin-insensitive but were significantly blocked by D-600 (10(-5) M) (an L-type Ca2+ ch annel blocker) or in Ca2+-free medium. Our data suggest that alpha-tri nositol has a plasmalemmal mechanism of action which could involve Ca2 + influx from the extracellular space.