The role of inositol 1,3,4,5-tetrakisphosphate in internal Ca 2+ mobilization following histamine H 1 receptor stimulation in DDT1 MF-2 cells

Abstract

Receptor-activated formation of inositol phosphates results in mobilization of intracellular stored Ca 2+ in a variety of cells, including vas deferens derived DDT 1 MF-2 cells. Stimulation of the histamine H 1 receptor on these cells caused a pronounced formation of inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P 4) with respect to that of inositol 1,4,5-trisphosphate (Ins(1,4,5)P 3). In this study, the role of inositol phosphates, in particular Ins(1,3,4,5)P 4 on the internal Ca 2+-releasing process was investigated in permeabilized and histamine-stimulated intact DDT 1 MF-2 cells. In permeabilized cells, Ins(1,4,5)P 3 induced a concetration-dependent release of intracellular stored Ca 2+. Addition of Ins(1,3,4,5)P 4 did not cause Ca 2+ mobilization, but its presence enhanced the amount of Ca 2+ released by Ins(1,4,5)P 3, thereby increasing the total Ca 2+-releasing capacity. The effect of both inositol phosphates was inhibited by heparin, known to block Ins(1,4,5)P 3-sensitive receptors. Thus, the additional amount of Ca 2+ released by Ins(1,3,4,5)P 4 is mediated, either via Ins(1,4,5)P 3-sensitive Ca 2+ channels, or via different heparin-sensitive Ca 2+ channels activated by both Ins(1,4,5)P 3 and Ins(1,3,4,5)P 4. Histamine H 1 receptor stimulation in intact cells induced a Ca 2+-dependent K + current, representing Ca 2+ release from internal stores if receptor-activated Ca 2+ entry from the extracellular space was prevented under Ca 2+-free conditions or in the presence of La 3+. This transmembrane current was abolished in the presence of intracellularly applied heparin. Depletion of Ins(1,4,5)P 3-sensitive Ca 2+ stores by internal application of Ins(1,4,5)P 3 reduced the histamine evoked K + current to some extent if the contribution of external Ca 2+ was excluded. However, depletion of both Ins(1,4,5)P 3 and Ins(1,3,4,5)P 4-sensitive Ca 2+ compartments in advance caused abolition of the histamine-activated Ca 2+ regulated K + current. These results show that Ins(1,3,4,5)P 4 plays an important role in the Ca 2+-releasing process in DDT 1 MF-2 cells. It contributes to the development of the intracellular Ca 2+ signal following histamine H 1 receptor stimulation by enhancing the total Ins(1,4,5)P 3-sensitive Ca 2+-releasing capacity via a discrete Ca 2+ compartment.