Agonist-induced Ca2+mobilization in cultured bovine and human corneal endothelial cells

We investigated the possibility that cultured corneal endothelial cells express receptors that are coupled to the phosphoinositide cycle/intracellular Ca2+ signaling pathway. Agonist-stimulated changes in intracellular calcium ([Ca2+]i) in single bovine and human corneal endothelial cells (BCEC and HCEC, respectively) derived from confluent cultures were measured by microspectrofluorimetry using the Ca(2+)-sensitive probe, fura-2. Total inositol phosphates accumulated during a 30 min incubation in the presence or absence of agonists was determined in Li+ containing medium with cells pre-labelled for 48 hrs with 10 microCi/ml 3H-myoinositol. Histamine (HA), ADP and ATP induced a rapid increase in [Ca2+]i. Subsequently, [Ca2+]i decreased to either a stable, agonist-dependent sustained elevation, or fell back to baseline to begin oscillatory fluctuations. The initial rise in [Ca2+]i was insensitive to removal of extracellular calcium (Ca2+o), whereas the stable elevations in [Ca2+]i and the [Ca2+]i oscillations required Ca2+o. In contrast, bradykinin (BK) and endothelin-1 (ET-1) elicited an initial rise in [Ca2+]i that returned to prestimulatory levels within 2 min despite the continued presence of agonist. The Ca(2+)-mobilizing agonists carbachol, phenylephrine, adenosine and substance P were all ineffective in elevating [Ca2+]i. Histamine-induced Ca2+ mobilization was inhibited by the H1-receptor antagonist triprolidine, but triprolidine had no effect on either BK or ATP stimulation of Ca2+ mobilization. In BCEC, 100 microM HA significantly increased total inositol phosphate accumulation (18.8-fold over unstimulated controls) and was 90% inhibited by 0.5 microM triprolidine. BK and ATP also significantly increased formation of inositol phosphates in BCEC.(ABSTRACT TRUNCATED AT 250 WORDS)