Abstract: | 1. The ionophore X-537A increases the rate of catecholamine release from the frog adrenal.2. The ratio of epinephrine/norepinephrine measured during X-537A stimulation was the same as that during spontaneous release.3. Even when Ca++ was removed from the Ringer, X-537A stimulated catecholamine release, but depolarization by elevated extra-cellular K+ was no longer effective.4. X-537A also increases the release of dopamine β-hydroxylase, suggesting that the ionophore acts, at least in part, by stimulating the exocytosis of the chrommaffin granule contents.5. Therefore, it is questionable whether the release of catecholamines by X-537A is owing to its action as a Ca++- ionophore.6. The divalent cation ionophore, A-23187 (50μM), did not affect the rate of catecholamine release. |