Ouabain-evoked norepinephrine release from intact rat sympathetic neurons: evidence for carrier-mediated release.
Inhibition of the Na,K-ATPase is known to cause transmitter release from many neurons. The mechanism of [3H]norepinephrine release was examined in primary cultures of sympathetic neurons. Ouabain caused [3H]norepinephrine release at concentrations that produced 80 to 90% inhibition of Na,K-ATPase activity. The effect of ouabain was compared with the effects of high K+ and the Ca2+ ionophore A23187. [3H]Norepinephrine release elicited by depolarization with high extracellular K+ was dependent on extracellular Ca2+, was unaffected by tetrodotoxin, was potentiated by reducing extracellular Na+, and was potentiated by the norepinephrine uptake inhibitor desipramine. These are the results expected if high K+ causes release by exocytosis, and if blockade of the Na+-dependent norepinephrine uptake system increases the net measurable release of the transmitter. The Ca2+ ionophore A23187 caused [3H]norepinephrine release that was not dependent on extracellular Ca2+ but which was like the release elicited by high K+ in other respects. Release elicited by ouabain was independent of extracellular Ca2+, was delayed for several hours by tetrodotoxin, was inhibited by reducing the concentration of extracellular Na+, and was inhibited by desipramine. These results suggest that the measured increase in transmitter release is secondary to a rise in the concentration of intracellular Na+. The data are consistent with the hypothesis that at high levels of pump inhibition, ouabain elicits nonvesicular [3H]norepinephrine release through reversal of the Na+-dependent plasma membrane carrier.
Sweadner
K J
KJ
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology*; D009474:Neurons / Q000201:enzymology / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013564:Sympathetic Nervous System / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D002352:Carrier Proteins; D000001:Calcimycin; D010042:Ouabain; D014701:Veratridine; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine