Responses of the transmembrane potential coupled to the ATP-evoked catecholamine release in isolated chromaffin granules.
Using suspensions of chromaffin granules isolated from bovine adreno-medullae, the effects of Mg2+.ATP on membrane potential and catecholamine release across membranes of granules were investigated. The release of catecholamine was monitored by the measurement of changes in endogenous fluorescence of the amines, while the fluorometric method with 3,3'-dipropylthiadicarbocyanine iodide (diS-C3-(5)) was applied to the measurement of membrane potential changes. The catecholamine release brought about by Mg2+.ATP was found to obey Michaelis-Menten kinetics with Km-value for Mg2+ of about 0.15 mM and to be inhibited by dicyclohexylcarbodiimide (DCCD), an inhibitor of membrane-bound H+-ATPase. Concomitantly with such an amine release, depolarization of the granule membrane was observed to occur. The magnitude of this depolarization closely paralleled with the rate of the amine release and followed a saturation kinetics of Michaelis-Menten type with Km for Mg2+ of 0.21 mM and for ATP of 0.22 mM. Moreover, such a depolarization was competitively suppressed by DCCD. Based on these results, the role of the transmembrane potential change of granules in the catecholamine release was discussed.
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000313:Adrenal Medulla / Q000166:cytology; D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002837:Chromaffin Granules / Q000378:metabolism*; D002838:Chromaffin System / Q000378:metabolism*; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D013050:Spectrometry, Fluorescence
D002395:Catecholamines; D004024:Dicyclohexylcarbodiimide; D000255:Adenosine Triphosphate; D008274:Magnesium