ИСТИНА

Special feature of smooth muscle cells (SMC) is that opening of Cl- channels leads to Cl- efflux and depolarization of the cell which enhances contraction. The role of Cl- currents may change during postnatal development: in antenatal and early postnatal neurons activation of GABA(A) receptors results in exit of Cl- and depolarization, while in mature neurons it leads to entrance of Cl- and hyperpolarization. It is still unknown if the role of chloride changes in arteries during postnatal development and what factors may lead to this change. Some changes of cardiovascular system during maturation are attributed to sympathetic nervous system (Puzdrova et al. 2014). In this study, we tested the hypothesis that the role of Cl- in the regulation of arterial contractile responses differs in young and adult rats due to the trophic action of sympathetic innervation. We used the young (10-14 days old) and adult (2-4 months old) male Wistar rats. In order to reveal trophic action of sympathetic nervous system we used 2 months old rats that were subjected to chronic neonatal sympathectomy with the use of guanethidine (Johnson, O’Brien, and Werbitt 1976) and compared them to control animals that got 0,9% NaCl injections. We registered contractile responses of endo- thelium-denuded saphenous artery in isometric myograph (DMT A/S) that were evoked by the cumulative addition of the α1-adrenoreceptor agonist methoxamine (MX, 10-8-10-4 M). The role of Cl- was studied by Cl- removal from the solu- tion (equimolar substitution of NaCl and KCl by respective aspartate salts). Comparison of NKCC1, AE2, and Cl- channels (TMEM16A and Bestrophin 3) mRNA expression levels in the saphenous arteries without endothelium were studied by RT-PCR (GAPDH, 18S and RPLP0 as reference genes). Removal of Cl- decreased effects of MX stronger in arteries of young rats (66% decline of force response, n=9) compared to adults (32% decline of force response, n=13) (t-test, p=0,001) and in sympathectomized rats (33% decline of force response, n=8) compared to control rats (18% decline of force response, n=8) (t-test, p=0,002). mRNA expression of NKCC1 (Mann-Whitney test, p=0,003), TMEM16A (t-test, p=0,03) and Bestrophin 3 (Mann-Whitney test, p<0,0001) were higher in young (n=9) compared with adult (n=8), AE2 did not differ between adult and young animals. The mRNA expression level of these genes did not differ between sympathectomized and control rats. Hence, the impact of Cl- on contractile responses of rat saphe- nous artery decreases during early postnatal development at least in part due to trophic action of sympathetic innervation. Johnson, Eugene M., Ferdinand O’Brien, and Rand Werbitt. 1976. “Modification and Characterization of the Permanent Sympathec- tomy Produced by the Administration of Guanethidine to Newborn Rats.” European Journal of Pharmacology 37: 45–54. Puzdrova, V. A., T. V. Kudryashova, D. K. Gaynullina, S. V. Mochalov, C. Aalkjaer, H. Nilsson, A. V. Vorotnikov, R. Schubert, and O. S. Tara- sova. 2014. “Trophic Action of Sympathetic Nerves Reduces Arterial Smooth Muscle Ca2+ Sensitivity during Early Post-Natal Development in Rats.” Acta Physiologica 212 (2): 128–41. Study was supported by RFBR (grant N 18-015-00216-a).