Histamine breaks down barrier integrity in corneal endothelial cells by phosphorylation of the regulatory light chain of myosin II. We hypothesize that histamine influences intercellular communication (IC) similar to the thrombin-induced inhibition of IC. In this study we investigated the effect of histamine on gap junctional (GJIC) and paracrine intercellular communication (PIC) in cultured bovine corneal endothelial cells (BCEC).

Cell-cell communication was investigated by intercellular Ca²⁺ wave propagation. Changes in [Ca²⁺]_i in the mechanically stimulated cell and in the neighboring cells were visualized using the fluorescent dye Fluo-4. The area reached by the Ca²⁺ wave (active area) was used as a measure of [Ca²⁺]_i. GJIC was assessed by fluorescence recovery after photobleaching (FRAP). Activity of hemichannels was assayed by Lucifer Yellow (LY) uptake and also by ATP release using the Luciferin-Luciferase technique. RT-PCR was used to examine the expression of histamine receptors (HRs).

RT-PCR showed transcripts for HR1 and HR2. Histamine reduced the active area of the Ca²⁺ wave. Histamine did not significantly reduce the fluorescence recovery in FRAP experiments. Activation of HRs did not affect Ca²⁺ wave propagation in cells pretreated with Gap26, which blocks connexin43 (Cx43) hemichannels. Pretreatment with Gap27 which inhibits Cx43 gap junctions, decreased the effect of HR activation on the active area. Histamine abolished the enhancement of the Ca²⁺ wave propagation by the ecto-nucleotidase inhibitor ARL-67156. The effect of histamine on the Ca²⁺ wave was not detectable in cells pretreated with exogenous apyrases. Exposure of BCEC to histamine under Ca²⁺ -free medium led to complete inhibition of LY uptake. Therefore, our results indicate that histamine inhibits the opening of hemichannel. Histamine markedly reduced ATP release upon mechanical stimulation (median reduction of 51%; N = 8), indicating that histamine the hemichannel-mediated PIC pathway. In conclusion histamine inhibits IC in BCEC. The effect is mainly through inhibition of the ATP-mediated PIC pathway. Histamine did not significantly inhibit the GJIC pathway.