Abstract
The purpose of the study was to investigate the influence of preactivation, wall tension and geometry on the reactivity of porcine coronary arteries to nifedipine and extracellular Ca 2+ in vitro. Porcine large coronary arteries were mounted as ring and cylindrical preparations and studied by wire- and balloon-based techniques. The sensitivity and maximal responses to nifedipine were more pronounced in 25 mM K + compared to 10 μM prostaglandin F 2α-contracted preparations. Vascular sensitivity to nifedipine and Ca 2+ was enhanced under isometric compared to isobaric conditions. Under isometric conditions in the presence of 25 mM K +, coronary rings were more sensitive to nifedipine, but less sensitive to Ca 2+ compared to cylindrical segments. In cylindrical segments, circumferential and axial tension increases augmented the extracellular Ca 2+-dependent spontaneous resting tone and the sensitivity to extracellular Ca 2+. Coronary rings showed no resting tone at various resting tensions. These results suggest that preactivation, wall tension and vessel geometry are important determinants of Ca 2+-influxes via nifedipine-sensitive voltage-gated Ca 2+ channels. Furthermore, axial wall tension appears to be a modulator of nifedipine-insensitive transmembrane Ca 2+-influx that may play a role for the tone and reactivity in large coronary arteries.
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