title: Activation and inhibition of calcium-dependent histamine secretion by ATP ions applied to rat mast cells.
abstract: 1. The concentration dependence on ATP of mast cell histamine secretion in the presence of various concentrations of Mg2+ and Ca2+ confirms that the agonist form of ATP is the free form of ATP (ATP(free) not bound to divalent cations, i.e. ATP4-. It induces 50% activation at about 1.2 microM, maximal secretion at about 2.7 microM and 50% self-inhibition at about 4.4 microM. 2. The divalent cations Mg2+ and Ca2+ were used to buffer ATP(tree) in the range 1-8 microM in the presence of much higher concentrations of ATP(total). In addition to its effect as a buffer for ATP, Ca2+ is required for secretion. 3. With ATP(free) at 1 microM, the time-course of histamine secretion is characterized by a delay of about 10 min before secretion commences. With increasing concentration of ATP(free) the delay becomes shorter (less than 5 min with ATP(free) at 2 microM). 4. Secretion commences promptly on addition of Ca2+ to cells which have been pretreated with low concentrations of ATP(free) (less than 2 microM). This observation suggests that the delay normally observed represents the time taken for Ca2+ sensitivity to develop (i.e. probably the time taken for Ca2+ channels to open). 5. Late addition of Ca2+ to cells pretreated with higher concentrations of ATP(free) (greater than 2 microM) results in a reduced amount of histamine secretion compared with that which normally occurs. This reduction (which increases with time of exposure to ATP) and the self-inhibition due to higher concentrations of ATP(free) may be two facets of a common inhibitory mechanism. 6. These results are discussed in the light of other experiments which show that mast cells treated with ATP(free) at self-inhibitory concentrations become permeable to phosphorylated metabolites and nucleotides.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006636:Histamine Release / Q000187:drug effects*; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008407:Mast Cells / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012636:Secretory Rate / Q000187:drug effects
chemical_list: D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium