ISSN:
0091-7419
Keywords:
secretory granules
;
ATP-induced lysis
;
osmotic gradient
;
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
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: 1It is a saturable function of ATP with half-maximal rates observed at 0.5 ± 0.1 mM ATP.2It is temperature dependent, eg, r = 6.1 ± 2.1%/min at 30°C vs 12.2 ± 2.5%/min at 37°C.3It 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.4It shows a nucleotide preference of ATP = GTP 〉 ADP 〉 AMP 〉 CTP = ITP.5It has an anion requirement.The above findings, combined with reports of ATP-induced lysis of cholinergeric, 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 to 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.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400130303
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