Calcium-dependent photodynamic action of di- and tetrasulphonated aluminium phthalocyanine on normal and tumour-derived rat pancreatic exocrine cells.

Important differences exist in the responses to photodynamic agents of normal and tumour-derived pancreatic acinar cells. In the present study amylase release has been used to assess the mechanisms by which the photodynamic drugs tetra- and disulphonated aluminium phthalocyanine (A1PcS4, A1PcS2) act on pancreatic cells via energy and calcium-dependent activation and transduction pathways. The photodynamic release of amylase was found to be energy dependent and inhibited by the chelation of free cytoplasmic calcium but not by the removal of extracellular calcium. In contrast to their effects on normal acinar cells, the photodynamic action of A1PcS4 and A1PcS2 was to inhibit amylase secretion from pancreatoma AR4-2J cells. Removal of extracellular calcium reversed this inhibitory effect on AR4-2J cells and produced a significant increase in amylase release, but chelation of free cytoplasmic calcium did not affect the inhibitory photodynamic action of the phthalocyanines on amylase release from the tumour cells. Overall, these results demonstrate further important distinctions between the photodynamic action of sulphonated aluminium phthalocyanines on normal versus tumour exocrine cells of the pancreas and indicate that calcium plays an important role in photodynamic drug action, since these agents affected intracellular calcium mobilisation at some distal point in the membrane signal transduction pathway for regulated secretion. Furthermore, the photodynamic inhibition of constitutive secretion in tumour cells may involve a calcium-dependent membrane target site or modulation of membrane calcium channels by activation of protein kinase C.

Immunoglobulin-G-dependent stimulation of guinea pig lung mast cells and macrophages.

Alveolar macrophages and mast cells isolated from guinea pig lung were passively sensitized with IgG1, IgG2, or serum obtained from guinea pigs actively sensitized with ovalbumin. The release of histamine by mast cells and of thromboxane A2 by alveolar macrophages upon ovalbumin challenge indicated that both antibodies and serum were capable of sensitizing these cells with similar effectiveness. Heating the serum at 56 degrees C for 4 h to inactivate IgE did not modify the antigen-dependent response of lung cells. These results suggest a predominant role for IgG in the allergic response of the guinea pig through the activation of different cell types such as lung mast cells and alveolar macrophages.

Photodynamic drug action on isolated rat pancreatic acini. Mobilization of arachidonic acid and prostaglandin production.

Chloro-aluminium phthalocyanine sulphonate (SALPC) when photon-activated generates singlet oxygen, elicits amylase release and causes plasma membrane permeabilization of pancreatic acinar cells (Matthews and Cui, Biochem Pharmacol 39: 1444-1457, 1990). Amylase release precedes membrane permeabilization suggesting that the initial release of amylase may be due to direct stimulation by singlet oxygen of secretagogue receptors or their coupled guanine nucleotide binding proteins (G-proteins) and effector systems including phospholipase A2 (PLA2). The aim of the experiments reported here was to establish the extent to which PLA2 activation, arachidonic acid mobilization, and prostaglandin production are involved in the photon-induced action of SALPC on dispersed, perifused acini isolated from the rat pancreas. The mobilization of arachidonic acid by a major secretory stimulant of pancreatic exocrine cells, cholecystokinin octapeptide, was also assessed: it produced a time- and concentration-dependent (10(-10)-10(-6) M) stimulation of arachidonic acid output from acini prelabelled with [1-14C]arachidonic acid. In contrast, the kinetics of arachidonic acid mobilization with photon-activated SALPC 1 microM, 4500 or 18,400 lux light intensity (lambda > 570 mm), was biphasic, an intensity-dependent stimulation being preceded by a more immediate initial inhibition of output. Light activation of SALPC and singlet oxygen generation may evoke the stimulatory phase of arachidonic acid release by an action on G-proteins, or by PLA2 activated directly, or via calcium influx, because NaF 20 mM, mellitin 2 mg/mL and the calcium ionophore A23187 1 microM caused a 2.9-, 33- and 5-fold increase, respectively, in arachidonic acid output. However, not only was the arachidonate stimulation delayed in response to SALPC but in other experiments designed to gain more insight into the turnover of arachidonic acid and its metabolites, the photodynamic release of amylase preceded maximum prostaglandin E2 (PGE2) output and amylase release was completely unaffected when PGE2 production was blocked by the cyclo-oxygenase inhibitor, indomethacin 10 microM. It is therefore likely that the rapid initial photodynamic release of amylase from pancreatic acini induced by SALPC is mediated by activation of the signal transduction pathway involving the release of intracellular calcium; arachidonic acid mobilization and prostanoid production may then be linked to the longer-term, cytolytic action of SALPC, especially in tumour cells.

On the mechanism of action of sodium orthovanadate in inducing histamine release from rat peritoneal mast cells.

Sodium orthovanadate produced a dose-dependent release of histamine and prostaglandin D2 from rat peritoneal mast cells. The release of histamine was selectively inhibited by the anion channel blockers SITS and DIDS, and by theophylline and dibutyryl cyclic-AMP, but was unaffected by disodium cromoglycate and lanthanum ions. Unlike IgE-directed ligands, vanadate did not produce any change in the intracellular concentration of cyclic-AMP but did promote a substantial uptake of calcium-45 from the incubation medium. This effect paralleled the release of histamine. These results are discussed in terms of the possible mode of action of vanadate.

Characteristics of histamine secretion from mast cells stimulated with sodium orthovanadate and other vanadium compounds.

Sodium orthovanadate was found to be an effective histamine liberator from serosal mast cells of the rat and mouse. The release process was slow, non-cytotoxic and strongly dependent on pH and extracellular calcium. The effect was highly tissue and species specific and human basophil leucocytes, human lung mast cells and tissue mast cells of the rat and guinea pig were only weakly responsive or essentially unreactive. Other oxyanions of vanadium with the metal in the (+V) oxidation state also evoked histamine release from rat peritoneal mast cells but neither vanadyl sulphate (+IV oxidation state) nor the analogous orthophosphate anion were effective secretagogues. On the basis of these results, the possible mechanism of action of vanadate is discussed.

Some further characteristics of histamine secretion from rat mast cells stimulated with sodium orthovanadate.

Sodium orthovanadate induced a release of histamine from rat peritoneal mast cells. Other oxyanions of vanadium with the metal in the +V oxidation state also evoked histamine release but neither vanadyl sulphate (+IV oxidation state) nor the analogous orthophosphate anion were effective secretagogues. The release evoked by vanadate was selectively inhibited by the anion channel blocker SITS, and by theophylline and Bu2cAMP, but was unaffected by disodium cromoglycate and lanthanum ions. These results are discussed in terms of the possible mode of action of vanadate.

Effects of sodium cromoglycate and nedocromil sodium on histamine secretion from mast cells from various locations.

Nedocromil sodium and sodium cromoglycate inhibited histamine release from rat peritoneal mast cells. Tachyphylaxis was observed with both drugs. The 2 compounds were extremely selective in their action, being less active against peritoneal mast cells from the hamster and completely ineffective against mast cells from the mouse. Human basophil leucocytes, tissue mast cells of the guinea-pig and rat intestinal mast cells were also unresponsive. Both drugs inhibited immunological histamine release from human pulmonary mast cells obtained by bronchoalveolar lavage (BAL) and, less effectively, from lung parenchyma. Nedocromil sodium was about 1 order of magnitude more potent than sodium cromoglycate in each case. Tachyphylaxis was observed with the dispersed lung, but not with the cells obtained by BAL, and the degree of inhibition varied inversely with the magnitude of the secretory response. The possible clinical significance of these observations is discussed.

Histamine secretion from mast cells stimulated with sodium orthovanadate.

Sodium orthovanadate was found to be an effective histamine liberator from peritoneal mast cells of the rat and mouse. The release process was slow, non-cytotoxic and strongly dependent on pH and extracellular calcium. The effect was highly tissue and species specific and human basophil leucocytes and tissue mast cells of the rat and guinea pig were only weakly responsive or essentially unreactive.