Modulation of chaotic pressure oscillations in isolated resistance arteries by EDRF

By using non-linear techniques to analyse irregular histamine-induced pressure oscillations in an isolated rabbit ear resistance artery, we have shown that the pressure oscillations are generated by deterministic rather than stochastic mechanisms. The average fractal dimension of the oscillations was between 2 and 3, thus implying that three (or more) independent control variables were necessary to account for the complexity of the dynamics. EDRF suppressed the pressure oscillations, but their fractal dimension was not altered by graded stimulation of EDRF activity by acetylcholine, or by inhibition of EDRF activity with NG-nitro-L-arginine methyl ester (L-NAME) or haemoglobin. This implies that EDRF is not one of the primary control variables involved in the genesis of their dynamics. The oscillations exhibited distinct 'fast' and 'slow' components, with periods of 5-20 s and 1-5 min respectively. The fast subsystem involved ion movements at the cell membrane level, and was inhibited by low [Ca2+]o, by verapamil (which inhibits voltage-dependent Ca2+ influx) and by tetraethylammonium (TEA) and apamin (which block Ca(2+)-activated outward K+ channels). In contrast, the slow subsystem was selectively inhibited by ryanodine, and therefore involved intracellular Ca(2+)-induced Ca2+ release. Each of these interventions decreased the fractal dimension to < 2 and thus removed one degree of freedom from the dynamics. We conclude that the interaction of a fast membrane oscillator and a slow intracellular oscillator generates chaotic pressure oscillations which are modulated by EDRF.