Interactions of Vasoactive Effects Adenosine and Potassium Ion on Isolated Feline Coronary Artery Smooth Muscle

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This study evaluated the interactions of adenosine and alterations in K+ concentration [K+] on isolated coronary artery smooth muscle. Helical strips of cat coronary arteries, suspended in physiologic salt solution (37 °C, 95% Oi, and 5% COi) were used. In some experiments, isometric tension was induced by acetylcholine (ACh), while in others, spontaneously contracting strips were studied. In the first 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 μM adenosine than were strips developing spontaneous tone. In the second series of 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. However, following the addition of adenosine, which produced a 20.4 ± 3.0% relaxation, a 2.0 mM increment of [K+] induced an additional relaxation of 29.7 ± 4.6%, which was significantly greater than the relaxation in the absence of adenosine (P < 0.005). Simultaneous addition of potassium and adenosine produced significantly greater relaxation than either substance individually. The latter two findings support the concept that vasoactive agents may interact to relax arterial smooth muscle. These results may have implications with regard to local regulation of coronary blood flow. Circ Res 44: 207-215, 1979

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