Differences and similarities in the noradrenaline- and caffeine-induced mechanical responses in the rabbit mesenteric artery
Abstract
1. The properties of noradrenaline (NA)-induced and caffeine-induced contractions in the rabbit mesenteric artery were investigated and compared, using intact and skinned muscles.2. NA (> 10(-7) M) depolarized the membrane and reduced the membrane resistance. Increased concentrations of NA (> 10(-5) M) rarely produced oscillatory potential changes yet consistently produced oscillatory contractions which were abolished by pre-treatment with prazosin or Ca-free solution. Application of low concentrations (0.5 mM) of caffeine hyperpolarized the membrane and high concentrations (5 mM) depolarized the membrane.3. NA- and caffeine-induced contractions, but not a K-induced contraction, could be recorded in Ca-free, EGTA (2 mM) containing solution.4. In Ca-free, EGTA containing solution, repetitive applications of NA or caffeine led to a cessation of contractions. Responses persisted longer with applications of NA than with caffeine. In Na-free, Ca-free solution, the contractions evoked by both agents applied repetitively persisted much longer than those evoked in the presence of [Na](o).5. When 50 mug/ml. saponin was applied for 8 min, NA produced only one contraction and with application of 10(-6) M-Ca, only a small contraction was e...Continue Reading
Citations
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