title: Mitochondrial release of Ca2+ during sustained nerve activity in the electric organ of Torpedo marmorata.
abstract: The calcium content of mitochondria isolated from the Torpedo electric organ was determined by atomic absorption spectroscopy. The mitochondrial fraction was found to contain 830 ng-atom Ca/mg protein. For comparison a fraction of isolated nerve endings contained 250 ng-atom Ca/mg protein. When tissue was continuously stimulated at a frequency of 5 Hz via the electromotor nerves, the Ca content of the mitochondrial fraction which is likely to contain both pre- and postsynaptic mitochondria was reduced proportionally to the decrease in transmitter content of the isolated nerve terminal fraction. After 5,000 pulses, the mitochondrial fraction had lost 80% of its Ca contents. When tissue was stimulated after previous perfusion with d-tubocurarine and blockade of electrical response the same number of pulses caused only a loss of 20--40% in the Ca content of the mitochondrial fraction. Release of transmitter was not affected by d-tubocurarine. The results suggest that repetitive stimulation in the absence of postsynaptic receptor blockade causes loss of Ca from both nerve terminal mitochondria and mitochondria of the myotube-derived electrocytes. In the presence of d-tubocurarine Ca is lost from presynaptic mitochondria only.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004557:Electric Organ / Q000294:innervation*; D004558:Electric Stimulation; D005399:Fishes; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects; D013574:Synaptosomes / Q000378:metabolism; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D000109:Acetylcholine; D002118:Calcium; D014403:Tubocurarine