title: Contribution of Na+ and membrane depolarization to contraction induced by adrenaline in the guinea pig vas deferens.
abstract: The contribution of Na+ and membrane depolarization to biphasic contractions induced by adrenaline were investigated in the smooth muscle of guinea pig vas deferens. Adrenaline (5 X 10(-6) M) produced an initial small contraction (first contraction) followed by a large tonic contraction (second contraction) with subsequent rhythmic activity. The entire response to adrenaline was largely inhibited by phentolamine (5 X 10(-6) M). By adding an appropriate concentration of Mn2+ (2 X 10(-4) M) or nifedipine (3 X 10(-7) M), a Ca2+ blocker, the second contraction was strongly reduced, accompanied by abolishment of the rhythmic contraction, whereas the first contraction was virtually unaffected. However, the first contraction was markedly suppressed by a higher concentration of Mn2+. All contractions produced by adrenaline were greatly reduced in Ca2+-free solution containing 0.5 mM EGTA. By lowering external Na+ concentration, the first contraction was markedly increased without greatly affecting the second contraction. By exposure to Na+-free isotonic high K+ solution, which elicited a greater depolarization of the membrane, the first contraction produced by adrenaline was also greatly potentiated, while the second and rhythmic contractions were eliminated. These results suggest that the adrenaline-evoked first contraction may be due to an influx of membrane bound Ca2+ which is independent of membrane depolarization, while the second (rhythmic) contraction is due to an influx of extracellular Ca2+ which is dependent upon depolarization.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D004837:Epinephrine / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008566:Membranes / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009467:Neuromuscular Depolarizing Agents; D009543:Nifedipine / Q000494:pharmacology; D012964:Sodium / Q000502:physiology*; D014649:Vas Deferens / Q000187:drug effects
chemical_list: D009467:Neuromuscular Depolarizing Agents; D008345:Manganese; D012964:Sodium; D009543:Nifedipine; D002118:Calcium; D004837:Epinephrine