Novel effects of a sleep‐inducing lipid, oleamide, on Ca2+signaling in renal tubular cells

The effect of oleamide, a sleep‐inducing endogenous lipid in animal models, on intracellular free levels of Ca2+([Ca2+]i) in Madin‐Darby renal tubular cells was examined using fura‐2 as a fluorescent dye. Oleamide (5–50 μM) increased [Ca2+]iin a concentration‐dependent fashion with an EC50value of 20 μM. The [Ca2+]isignal comprised an initial rise and an elevated phase and was reduced by removing extracellular Ca2+by 50%. After pretreatment with 5–50 μM oleamide in Ca2+‐free medium, addition of 3 mM Ca2+increased [Ca2+]iin a manner dependent on the concentration of oleamide. In Ca2+‐free medium, pretreatment with thapsigargin (1 μM), an endoplasmic reticulum Ca2+pump inhibitor, abolished [Ca2+]iincreases induced by 20 μM oleamide; conversely, pretreatment with 20 μM oleamide reduced 1 μM thapsigargin‐induced [Ca2+]iincreases by 50%. Suppression of the activity of phospholipase C with 2 μM U73122 abolished 20 μM oleamide‐induced Ca2+release. Collectively, these data demonstrate that oleamide induced significant [Ca2+]iincreases in renal tubular cells by a phospholipase C‐dependent release of Ca2+from thapsigargin‐sensitive stores and by inducing Ca2+entry via store‐operated Ca2+entry. Drug Dev. Res. 54:40–44, 2001. © 2001 Wiley‐Liss, Inc.