Effect of Ki on the Ko dependence of Na/K pump current in adult rat cardiac myocytes.
Effect of Ki on the Ko dependence of Na/K pump current in adult rat cardiac myocytes.
复制标题
Ki 对成年大鼠心肌细胞 Na/K 泵电流 Ko 依赖性的影响。
DOI：
10.1111/j.1749-6632.1992.tb43829.x
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发表时间：
1992
影响因子：
5.2
通讯作者：
Stimers,JR
中科院分区：
文献类型：
--
作者：
Kinard,TA;Stimers,JR
Our laboratory group is in the process of investigating how ions interact in regulating Na/K pump function and how these interactions affect the Na/K pump’s sensitivity to cardiac glycosides. Previously, we used the whole-cell patch-clamp technique to examine the effect of internal “a](Na,) on the external [K](K,,) dependence of the Na/K pump current (I,) in adult rat ventricular myocytes and found a Hill coefficient (n) of approximately 1 (FIG. 1, B).’To explore why n was not 2 as predicted by models of the Na/K pump, the effect of internal [K](Ki) was evaluated by altering the pipette [K](Kp) and keeping the pipette “a](Na,) constant at 30 mM (total monovalent cation concentration was 160 mM). Adult rat ventricular myocytes were isolated by digestion of Langendorf€ perfused hearts with collagenase. 2 The wholecell patch-clamp technique was used to measure I, in myocytes voltage clamped at-40 mV and maintained at 3PC. The external test solutions contained 1 mM Ba, 0.1 mM Cd, and 0 Ca to block Ca and K currents to improve the isolation of I,. Using a protocol described previ~ usly,~ the pump was initially deactivated in a K-free solution and then reactivated by brief applications of solutions containing K, ranging between 0.17 and 10.8 mM. The K, dependence of I, was measured as the change in holding current from baseline to the initial peak produced when I, was reactivated by brief applications of K, solutions. Currents were normalized to cell membrane capacitance to get pump current density and then were curve fitted with the Hill equation. The best fit parameter values for each data set are given in TABLE 1 Our initial hypothesis was that when &= 75 mM and K,= 0 mM, K, leaking out of the cell accumulated in the transverse tubules (t-tubules) and partially reactivated the Na/K pump. This reactivation then caused an underestimation of n in our experiment. To test this, &was replaced with an equimolar substitution of Cs,. This resulted in an increase of n from 1.1 to 1.3 (FIG. 1, 0; TABLE l), supporting the hypothesis; however, n was still lower than expected. As Cs is a Kmimic on the Na/K pump, it is possible that the high Cs,(130 rnM) might also be affecting our results. We therefore substituted tetramethylammonium (TMA) for Cs, which resulted in an almost twofold increase in maximal I,(Ipmax), but little change in the Hill coefficient (FIG. 1, O; TABLE 1). The 47% reduction in Ipmax in the presence of Cs internally can be explained by Cs inhibiting the maximum turnover rate of the Na/K pump by favoring the reverse reaction. However, the decrease (rather than increase) in n, although unexpected, may be complicated by the increase in Ipmax. It is possible that aThis work was supported by NIH Grants HL44660 and RR06564. bTo whom correspondence should be addressed.
