SELECTIVE POTENTIATION OF HISTAMINE H-1-RECEPTOR STIMULATED CALCIUM RESPONSES BY 1,4-DITHIOTHREITOL IN DDT(1)MF-2 CELLS

The effect of 1,4-dithiothreitol (DTT) on agonist-stimulated increases in intracellular free calcium concentration ([Ca2+](i)) has been investigated in the smooth muscle cell line, DDT(1)MF-2, derived from hamster vas deferens. Pretreatment with DTT (1 mM) produced a large leftward parallel shift in concentration-response curve far histamine H-1-receptor mediated increases in [Ca2+](i). The EC(50) values for H-1-receptor stimulated increases in [Ca2+](i) in the absence and presence of DTT were 11.3 +/- 1.5 mu M (N = 6) and 0.52 +/- 0.15 mu M (N = 6), respectively. DTT had no significant effect on the maximum Ca2+ response elicited by histamine (100 mu M). In the presence of DTT the partial H-1-receptor agonist 2-ppridylethylamine (100 mu M) increased [Ca2+](i) from 112 +/- 14 nM to 237 +/- 24 nM (N = 10). In control cells 2-pyridylethylamine (100 mu M) did not elicit a Ca2+ response. DTT had no significant effect on the maximum Ca2+ response elicited by 1 mM 2-pyridylethylamine. The enhancement of histamine H-1-receptor Ca2+ responses by DTT was reversed by the sulphydryl oxidizing agent dithiobis-(2-nitrobenzoic acid), DTT had no significant effect on adenosine A(1)-, bradykinin and ATP-receptor stimulated increases in [Ca2+](1). [H-3]mepyramine binding experiments confirmed that DTT increased agonist affinity. DTT produced a small, but significant, leftward shift in concentration-response curve for histamine displacement of [H-3]mepyramine binding. These data suggest that DTT potentiates H-1-receptor mediated Ca2+ responses by increasing agonist affinity.