Neuropeptide-induced cytosolic Ca2+ transients and phosphatidylinositol turnover in cultured human retinal pigment epithelial cells.
Neuropeptide-induced mobilization of cytosolic free Ca2+ concentration ([Ca2+]i) and phosphatidylinositol (PI) turnover in cultured human retinal pigment epithelial (RPE) cells were studied and their temporal relationship was compared. After RPE cells were loaded with fura-2/AM, [Ca2+]i was analyzed using a digital imaging microscopy system. Bombesin-related peptides which include bombesin, neuromedin B, and neuromedin C induced significant [Ca2+]i transients in RPE cells, whereas other neuropeptides, neuropeptide Y, vasoactive intestinal polypeptide (VIP), and substance P were not effective to produce [Ca2+]i transients. The percentage of reactive cells which showed positive [Ca2+]i transients induced by bombesin-related peptides was around 50%. Bombesin (1 microM) showed a peak concentration of 663 +/- 27.0 nM (mean +/- S.E.M., n = 61), neuromedin B (1 microM), 327 +/- 28.7 nM (mean +/- S.E.M., n = 38), and neuromedin C (1 microM), 357 +/- 22.7 nM (mean +/- S.E.M., n = 32). Ca2+ transients occurred within 30 s and lasted less than 5 min after the application of the neuropeptides. Chelation of the extracellular Ca2+ by EGTA significantly shortened the total time of [Ca2+]i transients induced by the above. The measurements of phosphoinositides in RPE cells revealed that neuropeptide-induced PI turnover was as quick as [Ca2+]i transients. Inositol biphosphate (IP2) and inositol triphosphate (IP3) in RPE cells showed transient increases at 15 s after the stimulation by bombesin-related peptides. These data show that changes in [Ca2+]i and PI turnover are directly linked and both are important in the signal transduction system of bombesin-related peptides in RPE cells. The data also suggest that bombesin-related peptides may play some possible roles in RPE cells.
Kuriyama
S
S
Department of Ophthalmology, Kyoto University Faculty of Medicine, Japan.
Yoshimura
N
N
Ohuchi
T
T
Tanihara
H
H
Ito
S
S
Honda
Y
Y
D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D009479:Neuropeptides / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D009479:Neuropeptides; D010716:Phosphatidylinositols; D002118:Calcium