Abstract
The binding of [ 125I]sarafotoxin 6b (SRT 6b) and [ 125I]endothelin-l (ET-1) to endothelin (ET) receptors of neuronal membranes prepared from cerebral cortex and spinal cord of 8-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) was determined. SHR had significantly higher blood pressure as compared to WKY. Heart rate was similar in SHR and WKY. [ 125I]SRT 6b and [ 125I] ET-1 bound to the membranes of cerebral cortex and spinal cord at a single, high affinity site. The binding of [ 125I]SRT 6b and [ 125I]ET-l in the cerebral cortex and spinal cord membranes was found to be similar in SHR and WKY. Concentration-dependent inhibition of [ 125I]ET-l binding in spinal cord membranes by unlabeled ET-1, ET-2 and ET-3 was performed. The K i values were found to be 2.35 ± 0.68, 0.29 ± 0.08 and 24.10 ± 5.90 nM for ET-1, ET-2 and ET-3, respectively in WKY. The K i values of ET-1 and ET-2 were found to be similar in WKY and SHR. However, the K i value of ET-3 were found to be significantly lower (P < 0.004) in SHR as compared to WKY. Concentration-dependent inhibition of [ 125I]SRT 6b binding in spinal cord membranes by unlabeled ET-1, ET-2 and ET-3 were also performed. The K i values were found to be 9.50 ± 2.10 pM, 0.17 ± 0.04 nM and 31.20 ± 6.00 nM for ET-1, ET-2 and ET-3, respectively in WKY. The K i values of ET-1 and ET-2 were found to be similar in WKY and SHR. However, the K i value of ET-3 were found to be significantly lower (P < 0.01) in SHR as compared to WKY. In the cerebral cortex inhibition of [ 125I]SRT 6b and [ 125I]ET-l binding by ET-3 was similar in WKY and SHR. It is concluded that in spinal cord ET receptors are of ET A type. It appears that there are two subtypes of ET A receptors in the spinal cord, ET A which are more selective to ET-1 as compared to ET-2 and ET A2 which are more selective to ET-2 as compared to ET-1. In SHR these receptors are more sensitive to ET-3 as compared to WKY and may be involved in the regulation of blood pressure.
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