The Effect Of Cold-induced Hypertension On VSMC BKCa Channel In Rats

OBJECTIVE:To observe the blood pressure and the current density of Large conductance calcium-activated potassium channel(BKCa) in Vascular Smooth Muscle Cells (VSMC) in the cold induced hypertensive rats, then to provide the theoretical foundation for prevention and treatment of hypertension in low temperature.METHODS:30 rats with the weight of (150-220)g SD(Sprague Dawley) were randomly divided into 5 groups(6 rats for each group). Control group rats were raised at room temperature (25±1)℃;The cold stressed group rats were exposed to cold surrounding(4±1℃,relative humidity of 70%) for 4 hours per day, total for 8 weeks. Systolic blood pressure (SBP) was measured weekly by tail-cuff technique. The cold stressed and control rats were sacrificed at the second, fourth, sixth and eighth week. Single aortic vascular smooth muscle cells of rats were obtained by enzymatic dissociation. The whole-cell patch clamp recording technique was used to record the change of BKca current of VSMC in rats.RESULTS:1) SBP of the cold exposed rats was increased. At the second week, a significant difference was shown in SBP between the cold—exposed and the control group, with SBP of(102.8±2.25) mmHg and (89.16±3.73) mmHg respectively (P<0.01). SBP in the cold exposed group at the fourth, sixth and eighth week was respectively (114.53±4.21) mmHg;(121.94±3.03)mmHg; (135.27±5.37) mmHg, which was significantly different from the control group(P<0.01).2), It was recorded by patch-clamp technique that the BKca peak current density of aortic vascular smooth muscle cells in cold exposed rats increased significantly as the time of exposure to cold went by. At the second week, a significant difference was shown in the BKca peak current density between the cold—exposed and the control group, with the BKca peak current density of(138.47±6.57)pA/pF and(79.79±4.80)pA/pF respectively (P< 0.01).At the forth, sixth and eighth week, the BKca peak current density in the cold exposed group raised to(211.29±8.11)pA/pF;(295.27±10.77)pA/pF;(355.23±4.55)pA/pF respectively, which was significantly different from the control group(P<0.01).3). The increase of BKca peak current density in aortic vascular smooth muscle cells of cold exposed rats was significantly correlated with the duration of the time exposed to cold and SBP (r=0.976,P<0.01)CONCLUSION:1) Cold stressed hypertension can be induced in rats after repeated exposed to cold.2) The increase of BKca peak current density in aortic vascular smooth muscle cells of cold exposed rats was significantly correlated with the duration of the time exposed to cold and SBP; 3) The increase of BKca current density in VSMC induced by cold stress indicated that the increase of VSMC Ca concentration was the possible hypertension pathogenesis of rats.