Effects of norepinephrine and isopentenyladenosine on Na^+/Ca^(2+) exchangecurrents in isolated guinea pig ventricular myocytes

目的：研究去甲肾上腺素（ＮＥ）和异丙肾上腺素（Ｉｓｏ）对Ｎａ＋／Ｃａ２＋交换电流的影响及受体调控机制．方法：应用全细胞电压钳技术的斜坡脉冲程序，测定离体豚鼠心肌细胞准稳态电流电压关系曲线．结果：ＮＥ０００５，００５和５μｍｏｌ·Ｌ－１分别使膜电位＋５０ｍＶ时的Ｎｉ２＋敏感电流增加２９％±９％，７２％±１１％和１２０％±３１％；Ｉｓｏ１５，１５０和１５００ｎｍｏｌ·Ｌ－１分别使该电流增加２８％±２８％，５６％±１３％和１０２％±１２％．ＮＥ和Ｉｓｏ的这种增强效应能被普萘洛尔１０μｍｏｌ·Ｌ－１完全阻断，而酚妥拉明５０μｍｏｌ·Ｌ－１无此作用．结论：ＮＥ和Ｉｓｏ通过兴奋心脏β肾上腺素受体使Ｎａ＋／Ｃａ２＋交换电流增加．

AIM: To study the effects of norepinephrine (NE) and isopentenyladenosine (Iso) on Na +/Ca 2+ exchange currents and the receptor mechanism. METHODS: The quasi steady state current voltage relationship from the isolated guinea pig ventricular myocytes was measured using whole cell voltage clamp techniques with a ramp pulse protocol. RESULTS: At potential of +50 mV, NE 0 005, 0 05, and 5 μmol·L -1 increased the Ni 2+ sensitive current by 29 % ±9 %, 72 %±11 %, and 124 %±31 4 %, respectively; Iso 1 5, 150, and 1500 nmol·L -1 caused increases in the Ni 2+ sensitive current by 2 8 % ±2 8 %, 56 %±13 %, and 102 %±12 %, respectively. Propranolol 10 μmol·L -1 completely inhibited the current changes induced by NE and Iso while phentolamine 50 μmol·L -1 showed no effects. CONCLUSION: NE and Iso increased the Na +/Ca 2+ exchange currents via stimulation of cardiac β adrenoceptor.