Bacteriorhodopsin and the purple membrane of halobacteria

Mast cells can be induced to secrete histamine by an ionophore, the action of which depends on the presence of calcium within a specific concentration range. The fact that labelled calcium can be seen to enter sensitized cells during histamine secretion in the presence of antigen suggests that the entry of calcium into the mast cell may be the trigger for the release of histamine.

Calcium Ionophores and Movement of Calcium Ions following the Physiological Stimulus to a Secretory Process

By subjecting isolated adrenal medullary cells to intense electric fields of brief duration it is possible to gain access to the cell interior without impairing the ability of the cell to undergo exocytosis. After a single exposure to a field of 2 kV/cm, τ=200 μsec, adrenal medullary cells behave as if their plasma membrane contains two pores of effective radius 2 nm. At 37°C these ‘equivalent pores’ remain patent for up to 1 hr. The formation and stability of these ‘pores’ is not affected by the Ca content of the bathing solution. The ‘pores’ permit externally applied catecholamine and Ca-EGTA to equilibrate rapidly with the cell water.

Calcium-dependence of catecholamine release from bovine adrenal medullary cells after exposure to intense electric fields.

Micromolar amounts of the divalent ionophore A23187 can activate echinoderm eggs. The activations by ionophore A23187 were examined in terms of membrane elevation, the program of membrane conductance changes, the respiratory burst, and the increases in protein and DNA synthesis which normally accompany activation by sperm. In all these respects activation by the ionophore was fairly normal although subsequent cleavage and embryonic development was limited. Ionophore A23187 activations of the cortex of Lytechinus pictus and Strongylocentrotus purpuratus eggs were compared in various ionic media and were found to be completely independent of the ionic composition of the external solution. Respiration and protein synthesis of L. pictus eggs in singly substituted ionic media also indicated that these activations were independent of external sodium, calcium, or magnesium. These results suggest that the ionophore acts by releasing intracellular Ca(++). Consistent with this interpretation is the finding that eggs preloaded with (45)Ca show a 20-fold increase in (45)Ca-efflux when activated by ionophore A23187 or fertilization. Measurements of the "free" and "bound" calcium and magnesium in homogenates of the unfertilized eggs show that most of the Mg(++) is already available in the soluble form, whereas Ca(++) is sequestered but available for release. We propose that both normal fertilization and ionophore activation affect the metabolism of the egg by releasing Ca(++) sequestered in intracellular stores.

https://www.pnas.org/content/pnas/71/5/1915.full.pdf

Activation of sea-urchin eggs by a calcium ionophore.

Rotational and lateral diffusion of membrane proteins.

A possible role for cyclic AMP in the regulation of histamine secretion and the action of cromoglycate

ALTHOUGH the effects of anaphylaxis and chemical histamine releasers are similar and mainly attributable to histamine release, the mechanism by which the release occurs in the two cases is fundamentally different. We have found that lack of oxygen and also inhibitors of oxidative and glycolytic metabolism have a powerful inhibitory action on the release of histamine in anaphylaxis but enhance its release by compound 48/80 (a condensation product of p-methoxyphenyl-ethyl-methylamine and formaldehyde) and octylamine.

Inhibition of histamine release in anaphylaxis.

THE release of histamine from mast cells is similar, in many respects, to other secretory processes. In common with transmitter release at the motor nerve terminal and catecholamine release from the adrenal medulla, histamine release is dependent on calcium ions1–4. Experiments have shown that the antigen-stimulated histamine release from rat peritoneal mast cells has two components: a larger component requiring the presence of calcium ions and a smaller one which is not reduced by removal of calcium ions from the incubating medium or by the addition of a calcium chelating agent (EDTA)4. Also “spontaneous release” of histamine, in the absence of antigen, is apparently independent of calcium. Lanthanum inhibits the action of calcium in certain tissues and van Breemen has shown that lanthanum blocks the movement of calcium across artificial membranes and smooth muscle cell membranes5,6. We wished therefore to study the action of lanthanum on histamine release from isolated rat peritoneal mast cells.

Dual Effect of Lanthanum on Histamine Release from Mast Cells

ZELLER1 has shown that semicarbazide inhibits histaminase We have found that this substance, added to Tyrode solution, potentiates the action of histamine on the guinea pig's ileum The lowest concentration at which semicarbazide clearly potentiates histamine is of the order of 10−9 The optimum concentration is approximately 10−6, when the size of the histamine contractions may be doubled Very high concentrations depress the effects of histamine Potentiation is rapidly established and readily reversible The accompanying record shows that semicarbazide selectively potentiates histamine, but has no similar effect on acetylcholine Semicarbazide alone produces no contraction of the ileum, and the potentiation is probably due to inhibition of histaminase Eserine, which inhibits, cholinesterase, potentiates the effect of acetylcholine on the ileum much more than that of histamine Certain other inhibitors of histaminase also potentiate histamine The most active compound hitherto found is 2-methyl-5-amino-methyl-6-amino-pyrimidine (B1 pyrimidine) which we have obtained through the kindness of Dr Bergel, of Roche Products, Ltd This compound potentiates histamine in a concentration of 2 × 10−10

J. L. Mongar

Papers

Calcium Ionophores and Movement of Calcium Ions following the Physiological Stimulus to a Secretory Process

A possible role for cyclic AMP in the regulation of histamine secretion and the action of cromoglycate

Inhibition of histamine release in anaphylaxis.

Dual Effect of Lanthanum on Histamine Release from Mast Cells

Potentiation of the action of histamine by semicarbazide.