Friis Ulla G, Madsen Kirsten, Svenningsen Per, Hansen Pernille B L, Gulaveerasingam Ambika, Jørgensen Finn, Aalkjaer Christian, Skøtt Ole, Jensen Boye L
Department of Physiology and Pharmacology, Institute of Medical Biology, University of Southern Denmark, DK-5000 Odense, Denmark.
J Am Soc Nephrol. 2009 Oct;20(10):2154-61. doi: 10.1681/ASN.2008090944. Epub 2009 Jul 23.
The mechanism by which extracellular hypotonicity stimulates release of renin from juxtaglomerular (JG) cells is unknown. We hypothesized that osmotically induced renin release depends on water movement through aquaporin-1 (AQP1) water channels and subsequent prostanoid formation. We recorded membrane capacitance (C(m)) by whole-cell patch clamp in single JG cells as an index of exocytosis. Hypotonicity increased C(m) significantly and enhanced outward current. Indomethacin, PLA(2) inhibition, and an antagonist of prostaglandin transport impaired the C(m) and current responses to hypotonicity. Hypotonicity also increased exocytosis as determined by a decrease in single JG cell quinacrine fluorescence in an indomethacin-sensitive manner. In single JG cells from COX-2(-/ -) and AQP1(-/ -) mice, hypotonicity increased neither C(m) nor outward current, but 0.1-muM PGE(2) increased both in these cells. A reduction in osmolality enhanced cAMP accumulation in JG cells but not in renin-producing As4.1 cells; only the former had detectable AQP1 expression. Inhibition of protein kinase A blocked the hypotonicity-induced C(m) and current response in JG cells. Taken together, our results show that a 5 to 7% decrease in extracellular tonicity leads to AQP1-mediated water influx in JG cells, PLA(2)/COX-2-mediated prostaglandin-dependent formation of cAMP, and activation of PKA, which promotes exocytosis of renin.
细胞外低渗刺激肾小球旁（JG）细胞释放肾素的机制尚不清楚。我们推测，渗透压诱导的肾素释放依赖于水通过水通道蛋白-1（AQP1）水通道的移动以及随后的类前列腺素形成。我们通过全细胞膜片钳记录单个JG细胞的膜电容（C(m)）作为胞吐作用的指标。低渗显著增加C(m)并增强外向电流。吲哚美辛、磷脂酶A2（PLA(2)）抑制以及前列腺素转运拮抗剂损害了对低渗的C(m)和电流反应。低渗还以吲哚美辛敏感的方式通过单个JG细胞喹吖因荧光的降低确定增加了胞吐作用。在来自环氧化酶-2（COX-2）基因敲除和AQP1基因敲除小鼠的单个JG细胞中，低渗既不增加C(m)也不增加外向电流，但0.1μM前列腺素E2（PGE(2)）在这些细胞中均增加二者。渗透压降低增强了JG细胞而非产生肾素的As4.1细胞中的环磷酸腺苷（cAMP）积累；只有前者有可检测到的AQP1表达。蛋白激酶A的抑制阻断了JG细胞中低渗诱导的C(m)和电流反应。综上所述，我们的结果表明，细胞外张力降低5%至7%会导致AQP1介导的水流入JG细胞，PLA(2)/COX-2介导的依赖前列腺素的cAMP形成以及蛋白激酶A的激活，从而促进肾素的胞吐作用。
