Effects of Acetylcholine and Calcium Ions on the Spontaneous Release of Epinephrine from Catecholamine Granules. ∗

Summary

The amount of epinephrine released spontaneously into the supernatant from suspensions of adrenal medullary granules incubated at 37°c for 10 minutes was significantly decreased in non-electrolyte media as compared to electrolyte media, The reaction (pH 6.5-7.4) had little influence. Addition of CaCl₂ (.25-2.5 mM) was ineffective in the sucrose suspensions; it caused slight but consistent effects in the electrolyte media only. There was a 10-15% increased release in the sodium containing media; there was a 10-15% decreased release in the potassium containing media, Addition of acetylcholine did not modify the calcium induced effects. Addition of EDTA did not modify the spontaneous release in the sodium containing medium. The insignificant to small changes (±15%) in the spontaneous release caused by addition of calcium ions in the in vitro system is discussed in relation to many times (100X) increased rate of secretion caused by addition of calcium ions in organ perfusion experiments.