Effects of histamine on inositol phosphates and intracellular Ca2+ in human glomerular epithelial cells

The effect of histamine on the phosphoinositide turnover andintracellular free calcium activity Ca²⁺]_i was examined inhuman glomerular epithelial cells in culture. Addition of histamineto glomerular epithelial cells resulted in formation of inositolphosphates in a time- and dose-dependent manner. A transientmaximum of inositol trisphosphate (InsP₃) was observed within10 s. Stimulation of protein kinase C by short-term pretreatment(15 mm) of glom erular epithelial cells with phorbol 12-mynstate13-acetate caused a dose-dependent inhibition of the histamine-inducedinositol phosphate accumulation. The baseline of Ca²⁺]_i inthe cells was 115 ±2.7 nmol/l (n=103). Histamine (ED₅₀:approx. 2x10^–7mol/l) caused a rapid and transient increasein Ca²⁺]_i, as detected by fura-2 microfluorimetry studies.In a calcium-free extracellular solution the rapid increaseof Ca²⁺]_i was still present. The H₁ receptor antagonist mepyramine(IC₅₀: approx. 8 x 10^–9 mol/l) inhibited the histamine(10^–6 mol/l) response on Ca²⁺]_i Cimetidine, a potentH₂ receptor antagonist, showed no effect. This data indicates that H₁ receptor activation causes hydrolysisof phosphatidylinositol 4, 5-bisphosphate by phospholipase Cactivation, and consecutive mobil ization of intracellular calcium.Since histamine is a mediator of inflammation, antigen responseand cellular injury, these findings could be of importance forthe understanding of glomerular epithelial cell pathology.