Background. Histamine is a nitrogenous compound that is crucial for the progression and initiation of the local inflammation-driven response. It has been shown that the levels of histamine are increased in renal diseases such as diabetic nephropathy and acute kidney injury. Although substantial histamine levels have been reported in the kidney, renal pathological and physiological effects of this compound are not clearly defined. In this study, we hypothesized that histamine is a crucial regulator of renal epithelial function through its effects on ion transport and actin cytoskeleton rearrangements.   

Methods. Immunostaining of cultured cells, human and rat tissues, combined with Western blotting, were employed to characterize the renal expression of histamine receptors (HRs) and histaminergic system (HiS) enzymes. The acute functional effects of histamine were tested in principle cortical collecting duct (mpkCCD) and opossum proximal tubule (OK) cells, immortalized human podocytes, and podocytes of isolated rat glomeruli. Functional confocal imaging was used to detect changes in intracellular Ca²⁺ (Fluo8/FuraRed). Actin cytoskeleton rearrangements were assessed by staining with rhodamine-phalloidin. Ion transport was probed with short-circuit current measurements and patch clamp. Differences between the groups were tested with ANOVA; p < 0.05 was considered significant.     

Results. We showed that all four HRs, as well as HiS enzymes (histidine decarboxylase (HDC), histamine-N-methyltransferase (HNMT), and diamine oxidase (DAO)), are present in the rat and human kidney cortex, with segment-specific nephron expression in glomeruli, proximal tubules, and collecting ducts. We further demonstrated the presence of all four HRs and HiS enzymes in cultured mpkCCD and OK cells. In mpkCCD, short-circuit current studies demonstrated inhibition of ENaC (epithelial Na⁺ channel)-mediated currents after 4 hours of incubation with histamine. Immunocytochemistry and qPCR confirmed this effect, showing a decrease in protein and gene expression for αENaC upon histamine treatment (n = 7/group, p < 0.05). In acute studies, single-channel patch clamp analysis revealed similar ENaC activity before and after histamine application (n = 6/group, p > 0.05). In response to histamine, we largely detected extracellular Ca²⁺ influx with a minor component of intracellular store depletion. Intracellular Ca²⁺ influx in response to acute stimulation of HR was observed in mpkCCD cells (EC50 90 ± 15 uM; pilot data allow us to speculate that the responses are mediated via HR3a and HR4), OK cells, podocytes of the freshly isolated rat glomeruli, and cultured human podocytes (at least n = 3/group, up to 40 replicates, p < 0.05). In all cell types, we observed a time-dependent formation of F-actin stress fibers and cortical polymerization of F-actin following incubation with 100 uM histamine for 1 and 4 hours (n = 3 experiments per group, p < 0.05).     

Conclusions. Rat and human renal epithelia demonstrate strong expression of HiS components. Functionally, histamine elicits Ca²⁺ transients and actin reorganization in the proximal tubule, collecting duct cells, and podocytes. These data support the notion that local renal production of histamine plays a role in epithelial physiological and pathophysiological function through effects on electrolyte reabsorption, cell polarity, sheer stress response, and epithelial barrier integrity and permeability.