Changes in cytosolic free Ca++ by histamine stimulation in isolated guinea-pig parietal cells (the second report)

It was demonstrated in our previous report that cytosolic free Ca++ concentration showed increase following histamine stimulation in the dose dependent manner, by double wave length excitation method using fura-2 as an intracellular Ca++ probe. In this paper, the investigation about the source of cytosolic free Ca++ coming out following histamine stimulation was performed. Both Ca++ channel blocker (Verapamil and Diltiazem) and an intracellular Ca++ antagonist (TMB-8) suppressed the increase of cytosolic Ca++ concentration following histamine stimulation. 10(-4)M verapamil, 10(-4)M diltiazem and 10(-4)M TMB-8 suppressed cytosolic Ca++ concentration from 355.9 +/- 5.7 nM to 213.8 +/- 4.9 nM, from 330.1 +/- 7.3 nM to 149.8 +/- 1.7 nM and from 324.9 +/- 6.1 nM to 151.3 +/- 3.8 nM respectively in the values at the point of 20 min after 10(-4)M histamine stimulation. The time course study revealed that the course of increase consisted of two components: the "initial rise" which was observed in the first 1 min. followed by the "continuous rise". The initial rise may reflect the Ca++ coming out from the intracellular Ca++ pool and the continuous rise may reflect the Ca++ flowed into cell from outside. Verapamil and diltiazem did not suppress the initial rise, while TMB-8 suppressed it. It is concluded that increase of cytosolic Ca++ concentration following histamine stimulation may be concerned with both extra- and intracellular Ca++ and that at first, intracellular Ca++ may be mobilized.