Osmotic Factors Determining the Release of Catecholamines from Isolated Chromaffin Cell Granules

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Abstract
Lishajko, F.Osmotic factors determining the releme of catecholamines from isolated chromaffin cell granules. Acta physiol. scand. 1970.79. 64–75.On incubation of bovine adrenal medullary granules in isotonic sucrose, KCl, NaCl or K‐phosphate, noradrenaline (NA) is initially released at a rapid rate followed by a slow exponential release. Adrenaline (A) release in the same media does not show the rapid initial phase. In hypotonic media both NA and A show a rapid initial release while in hyper‐tonic solutions both NA and A are released at a constant slow rate (t/2 = 115–185 min at 37°). Partial replacement of sucrose or dextrose media by NaCI, KCl or K‐phosphate decreases the release rate of Na and A. Addition of 6 mM Mg2+or Ca2+prevents the initial rapid fall of NA and of A in hypotonic solution. ATP‐Mg2+inhibits the release rate of catecholamines in chloride free media more than ATP or Mg2+alone. The granules were shown to shrink in the presence of divalent ions, as well as on addition of ATP or ATP‐Mg2+. During partial lysis or “osmotic shock” the granules lose slightly more A than NA. The results suggest that the NA containing granules from chromaffin cells initially possess a higher osmotic pressure than that of the A granules, possibly depending on the rate of splitting of an amine‐ATP‐complex. The release may depend partly on the ensuing osmotic equilibration process.