Mechanisms Underlying the Contractile Response to Endothelin-1 in the Rat Renal Artery
Authors: Callera Glaucia Elena , Bendhack Lusiane Maria 
Published: May 2003

We assessed the functional response and the mechanisms following receptor stimulation of endothelin-1 (ET-1) in the rat renal artery. In this study, isometric tension was recorded in renal artery rings without endothelium. Cumulative application of ET-1 from 0.1 to 100 nmol/l induced a sustained concentration-dependent contraction in the renal artery. Submaximal contraction induced by 10 nmol/l ET-1 in 2.5 mmol/l Ca<sup>2+</sup> and in the absence of inhibitors was used as control response (100%). The relative contribution of different sources of Ca<sup>2+</sup> in ET-1-induced contraction was evaluated. The contractile response to 10 nmol/l ET-1 in 2.5 mmol/l Ca<sup>2+ </sup>(1.2 ± 0.2 g) was significantly inhibited either in Ca<sup>2+</sup>-free solution containing 100 µmol/l ethylene glycol bis-(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (0.6 ± 0.1 g) or after depletion of intracellular Ca<sup>2+</sup> stores (0.62 ± 0.05 g). The contribution of phospholipase C and protein kinase C was evaluated by using their inhibitors 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate (NCDC) and [1-(5-isoquinolinesulfonyl)-2-methylpiperazine] (H-7), respectively. The contractile response to 10 nmol/l ET-1 was inhibited by 10 µmol/l NCDC (to 80 ± 6%) and 30 µmol/l H-7 (to 76.6 ± 6.5%). We found that 1 µmol/l nifedipine inhibited the ET-1-induced contraction (to 48.7 ± 6.9%), indicating the contribution of Ca<sup>2+</sup> influx through voltage-gated L-type Ca<sup>2+</sup> channels to this response. Further, the inhibitory effect of nifedipine was to a greater extent as compared with NCDC or H-7. Additive inhibition of ET-1-induced contraction was not observed in the presence of both nifedipine and NCDC. We also evaluated the role of the ionic transport system in the ET-1-induced response by using 20 nmol/l 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), an inhibitor of Na<sup>+</sup>-H<sup>+</sup> exchange, or 100 µmol/l ouabain, an inhibitor of Na<sup>+</sup>-K<sup>+</sup>-ATPase. The response to ET-1 was decreased by both EIPA (to 61.6 ± 8.4%) and ouabain (to 62.1 ± 8.6%). The contribution of Na<sup>+</sup>-Ca<sup>2+</sup> exchange to ouabain action was tested using the inhibitor dimethyl amiloride HCl (10 µmol/l). The decrease in ET-1-induced contraction by the combination of ouabain and dimethyl amiloride HCl was similar to that observed with ouabain alone. In view of these observations, both extra- and intracellular sources of Ca<sup>2+</sup> contribute to the contractile response induced by ET-1 in the renal artery. Our findings also revealed the importance of Ca<sup>2+</sup> influx through voltage-gated L-type Ca<sup>2+</sup> channels in mediating contraction to ET-1 in the renal artery, whereas a minor role of phospholipase C and protein kinase C was observed. Na<sup>+</sup>-H<sup>+</sup> exchange and Na<sup>+</sup>-K<sup>+</sup>-ATPase also play a role in the ET-1-induced contraction in renal artery. Moreover, the contribution of Na<sup>+</sup>-K<sup>+</sup>-ATPase in ET-1 contraction is not an Na<sup>+</sup>-Ca<sup>2+</sup> exchange-related process.