| Background:Essential hypertension is one of the most common cardiovascular diseases in our country. Currently, almost 290 million individuals are suffering from cardiovascular disease, and 270 million of these people have hypertension. Hypertension seriously threatens human health.The relaxation and contraction of vascular smooth muscle mainly determine the resistance in cardiovascular system. There are four common potassium channels in vascular smooth muscle participating in vascular response:voltage gated potassium channel (KV), Ca2+ activated potassium channel (KCa), inwardly rectifier potassium channel (Kir) and ATP sensitive potassium channel (KATP)-Previous studies suggest that the functional role of potassium channels is altered in hypertension, such as KV and Kir channels are functional decreased. However, in hypertension the changes and effects of VSMC KATP channel still are controversial.The KATP channel is composed of four hetero-octameric complex constituted of an inward rectifier potassium channel and four sulfonylurea receptor. KATP channels are the target of vasoactive molecules including various vasodilators such as H2S, calcitonin-gene related peptide, adenosine, prostacyclin, a-adrenoceptor agonist, vasoactive intestinal peptide and vasoconstrictors including angiotensin II, neuropeptide Y, noradrenaline, serotonin and endothelin. It is generally recognized that with the growth of age, vascular results in an increased response to vasoconstrictors and a decreased response to vasoactive molecules. Age is one of the independent risk factors of hypertension. In our previous study, we found six new mutation sites of KATP channel gene, which existed only in hypertension in Chinese elder people. Thus, we speculate that the changes of KATP channel expression and function with age may participate in the process of hypertension.Objective:We aim to study the change of expression and function of vascular smooth muscle cell KATP under hypertension situation at two different ages, in order to illuminate the effect of VSMC KATP in the development process of hypertension.Methods:Male SHR and WKY were randomly divided to four groups:16 weeks SHR,16 weeks WKY.49 weeks SHR,49 weeks WKY. Blood pressure was recorded by rail-cuff. VSMC KATP subunits expression was measured by real-time quantitative polymerase chain reaction detecting system (Q-PCR) and western bolt (WB) at mRNA and protein level, respectively.Isolated arteries rings were pre-contracted with 1 umol/1 phenylephrine (PE) in all groups, then successively added 10-9mol/l、10-8mol/l、10-7mol/l、10-6mol/l、10-5mol/l KATP activator including diazoxide, pinacidil to open channels. The changes of vascular rings’ tension were recorded. We used 5-hydroxydecanoate (5-HD) to block diazoxde and glibenclamide to block pinacidil, respectively, in order to test the vasodilation effect of diazoxide or pinacidil by opening KATP.Results:(1)There was no statistical difference between the same week-age SHR and WKY of body weight. (2)Blood pressure was increased in SHR groups when compared with the respective controls. No difference in blood pressure level was observed between 16 weeks and 49 weeks SHR. (3) at mRNA level, Kir6.1 expression was reduce by 35%in 16 weeks SHR group, a 38%decrease in 49 weeks SHR group, compared with 16 weeks SHR, there was a reduction about 25%in 49 weeks SHR. SUR2B expression was reduce by 26%in 16 weeks SHR group, a 61%decrease in 49 weeks SHR group, compared with 16 weeks SHR, there was a reduction about 51%in 49 weeks SHR.(P<0.05) (4) at protein level, Kir6.1 expression was reduce by 22%in 16 weeks SHR group, a 54%decrease in 49 weeks SHR group, compared with 16 weeks SHR, there was a reduction about 44%in 49 weeks SHR. SUR2B expression was reduce by 20%in 16 weeks SHR group, a 34%decrease in 49 weeks SHR group, compared with 16 weeks SHR, there was a reduction about 25%in 49 weeks SHR.(P<0.05). (5) The maximum vasodilation response of pinacidil was up to 93.84%. There was no statistical difference when compared the sensitivity of VSMC to pinacidil between age-matched SHR and WKY, and neither between the different age groups. (6) The maximum relaxing response of diazoxide was 48.72% and apparently weaker than pinacidil. No difference was observed in 16 weeks SHR aorta response to diazoxide compared with 16 weeks control (P>0.05). However, diazoxide caused marked lower relaxation in 49 weeks SHR compared with 49 weeks WKY in concentration of 10-6 mol/1 (12.06±0.61 vs 20.87±2.92, P<0.05) and 10-5 mol/1 (16.82±0.26 vs 48.72±4.31, P<0.001). (7)The pinacidil-induced relaxation was abolished by the KAtp blocker Gli (10 μmol/1) to a similar extent (P>0.05). Thus, the dAUC kept unchanged by Gli in both strains about AU986.65%-98.11%in both strains (8)MitoK.Arp channel inhibitor 5-HD blocked diazoxide-induced relaxation to a similar extent in SHR and normotensive rats (P>0.05).Conclusion:The expression of VSM KATP subunits Kir6.1 and sulfonylurea receptor (SUR2B) decreased during hypertension. Moreover, the expression of SUR2B and Kir6.1 in 49-week-old SHRs decreased much more than that in 16-week-old SHRs. Furthermore, the aorta rings of 49-week-old SHRs showed lower reactivity to diazoxide than 16-weekold SHRs. This study suggests that althoug the decrease of KATP is not directly coorelate with the increase of blood pressure, KATP channels in VSM subunits Kir6.1 and SUR2B contribute to modify the functionality of this channel in hypertension with age. |
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