Interactions of vasoactive effects of adenosine and potassium ion on isolated feline coronary artery smooth muscle.

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Abstract
The interactions of adenosine and alterations in K+ concentration [K+] on isolated coronary artery smooth muscle were studied. Helical strips of cat coronary arteries suspended in physiologic salt solution (37.degree. C, 95% O2 and 5% CO2) were used. In some experiments, isometric tension was induced by acetylcholine (ACh), and in others, spontaneously contracting strips were studied. In one series of experiments, equilibration of artery strips in solutions of increasing [K+] (2.0-10.0 mM) resulted in progressively decreasing responses to adenosine. ACh-stimulated strips were less responsive to 0.1-10.0 .mu.M adenosine than were strips developing spontaneous tone. In other experiments, [K+] was elevated abruptly in small increments both in the absence and presence of a background level of adenosine. From an initial concentration of 3.0 mM, a 2.0 mM increment of [K+] induced a transient relaxation of 16.0 .+-. 2.7% in the absence of adenosine. Following addition of adenosine, which produced a 20.4 .+-. 3.0% relaxation, a 2.0 mM increment of [K+] induced additional relaxation of 29.7 .+-. 4.6%, which was significantly greater than relaxation in the absence of adenosine (P < 0.005). Simultaneous addition of K+ and adenosine produced significantly greater relaxation than either substance alone. Vasoactive agents may interact to relax arterial smooth muscle and these results may be related to local regulation of coronary blood flow.