Calcium signaling and F-actin stability in the podocytes are regulated via activation of histamine receptors

Background: Inflammation is a crucial mechanism driving chronic kidney disease. One of the key mediators of inflammation is histamine; however, limited data are available regarding the role of the histaminergic system (HiS) in renal function. We have reported earlier that rodent and human kidneys express all components of the HiS, including histamine receptors (HRs). There is a gap in knowledge regarding the effects of histamine in the podocytes, which are key cells of the glomerular filtration barrier. We hypothesized that histamine activates HRs in the podocyte, leading to an increase in cytosolic Ca 2+ and the formation of actin stress fibers. Methods: Glomeruli freshly isolated from human (female) and Sprague-Dawley rat (male) kidneys were loaded with Fluo-8 for live confocal imaging. Intracellular Ca 2+ responses to acute applications of histamine (100 μM) were recorded in the podocytes following thapsigargin (1 μM) or vehicle in Ca 2+ -free or 2 mM Ca 2+ -containing solutions. H1R, H2R, H3R, and H4R inhibitors (5 μM cetirizine, 10 μM tiotidine, 10 μM JNJ-7207852, and 10 μM JNJ-7777120) and agonists (0.5 μM 2-pyridylethylamine, 1 μM dimaprit, 0.5 μM immethridine, or 0.5 μM 4-methylhistamine) were used to identify which receptors functionally contribute to Ca 2+ transients. To examine the contribution of Ca 2+ ionotropic extracellular influx, glomeruli were incubated with inhibitors for TRPC6 (1 μM BI-749327) and NMDA (5 μM MK-801). Cultured human podocytes were used for visualization of F-actin by rhodamine-phalloidin staining. OriginPro was used for statistical analysis. Results: Application of histamine produced fast Ca 2+ transients (2.5±0.2 au, τ decay = 11.4±2.0 s) in podocytes of both human and rat glomeruli. Specific agonists for H1R, H2R, and H4R, but not H3R, induced smaller amplitude Ca 2+ transients (1.9±0.2; 1.6±0.1; and 1.6±0.1 au, respectively). In rat glomeruli, pre-incubation with H1R and H2R inhibitors significantly reduced Ca 2+ transients (1.6±0.1 and 1.6±0.1 respectively, vs 1.9±0.1 au for vehicle controls, p< 0.05, ANOVA, Dunnet). Histamine application following the depletion of podocyte ER-Ca 2+ stores by thapsigargin caused negligible Ca 2+ responses (1.2±0.1 au). In Ca 2+ -free and 2mM Ca 2+ -containing solutions, we detected identical responses to histamine. Pre-incubation with either TRPC6 or NMDA inhibitors did not affect Ca 2+ responses to acute histamine applications, further suggesting the absence of extracellular influx in response to HR stimulation. In cultured human podocytes, we observed formation of ventral F-actin stress fibers following 4-hour incubation with 100 μM histamine. Conclusions: Histamine-induced Ca 2+ transients in the podocyte occur via activation of H1R, H2R, and H4R, and consecutive release from the ER. Prolonged exposure to histamine facilitates F-actin stress fiber formation in the podocyte. As HR inhibitors are available over the counter, understanding the effects of HR-targeting pharmacology is needed, as their usage may complicate renal disease treatment and clinical trial design. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.