title: ATP-induced lysis of rat parotid secretory granules: possible role of ATP in exocytotic release.
abstract: Secretory vesicles isolated from a variety of mammalian tissues are known to lyse and thereby release their secretory products when exposed to ATP. This process, which will be termed ATP-induced lysis, has been studied most extensively using adrenal chromaffin-granule preparations. We report here that ATP causes the lysis of a highly purified preparation of rat parotid secretory granules. The rate of granule lysis was measured spectrophotometrically, and ATP-induced lysis was expressed as the increase in the rate of lysis (r = % lysis per min) when ATP was added. This lytic process was characterized with respect to pH, temperature, osmolarity, and the ionic composition of the media. ATP-induced lysis of parotid granules was found to have the following properties in common with the extensively characterized chromaffin-granule process: 1. It is a saturable function of ATP with half-maximal rates observed at 0.5 +/- 0.1 mM ATP. 2. It is temperature dependent, eg, r = 6.1 +/- 2.1%/min at 30 degrees C vs 12.2 +/- 2.5%/min at 37 degrees C. 3. It is inhibited in hyperosmotic media, eg, r = 5.3 +/- 0.3%/min at 0.3 OsM vs 0.8 +/- 0.2%/min at 0.4 OsM. 4. It shows a nucleotide preference of ATP = GTP greater than ADP greater than AMP greater than CTP = ITP. 5. It has an anion requirement. The above findings, combined with reports of ATP-induced lysis of cholinergic, insulin, and posterior-pituitary vesicles, imply that ATP-induced lysis may reflect an ATP-dependent property of all secretory vesicles, and as such, this vesicle property could play a similar role in each exocytotic release process. Using a model system, Miller and Racker [22] made a surprising finding that the extent of which liposomes fuse with a black lipid membrane depends on the osmotic gradient across the vesicle membrane. In view of the osmotic dependence of ATP-induced lysis in this and other secretory-vesicle preparations, we postulate that ATP may prime secretory vesicles for fusion with the plasma membrane by inducing and/or maintaining an osmotic gradient across the vesicle membrane.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000681:Amylases / Q000032:analysis; D000818:Animals; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology*; D003576:Electron Transport Complex IV / Q000032:analysis; D005089:Exocytosis / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D008995:Monoamine Oxidase / Q000032:analysis; D009994:Osmolar Concentration; D010306:Parotid Gland / Q000502:physiology*; D011506:Proteins / Q000032:analysis; D051381:Rats; D012265:Ribonucleotides / Q000494:pharmacology
chemical_list: D011506:Proteins; D012265:Ribonucleotides; D000255:Adenosine Triphosphate; D008995:Monoamine Oxidase; D003576:Electron Transport Complex IV; D000681:Amylases