Yano K, Tsuda Y, Kaji Y, Kanaya S, Fujino T, Niho Y
First Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Jpn Circ J. 1994 Nov;58(11):836-43. doi: 10.1253/jcj.58.836.
Steroid hormones are thought to have a positive inotropic action, but the precise electrophysiological effects which underlie this positive inotropism remain unknown. The effects of hydrocortisone on the L-type calcium current (ICa) of the isolated guinea pig ventricular cells were investigated under the whole-cell voltage-clamp recording. Hydrocortisone (10(-6) to 10(-5) M) increased the amplitude of ICa without any changes in the voltage-dependency in ICa. This agent retarded the fast inactivation component of ICa, but not the slow component. On the other hand, hydrocortisone slightly reduced the slope conductance of inward rectifying potassium current (IK1) at potentials less than -50mV. This effect on IK1 is favorable for the activation of ICa. Thus, these results indicate that the positive inotropism of hydrocortisone is mediated, at least in part, by a direct potentiating effect on ICa.
类固醇激素被认为具有正性肌力作用，但其正性肌力作用背后的确切电生理效应仍不清楚。在全细胞电压钳记录下，研究了氢化可的松对分离的豚鼠心室细胞L型钙电流（ICa）的影响。氢化可的松（10（-6）至10（-5）M）增加了ICa的幅度，而ICa的电压依赖性没有任何变化。该药物延迟了ICa的快速失活成分，但不影响慢速成分。另一方面，氢化可的松在电位小于-50mV时略微降低了内向整流钾电流（IK1）的斜率电导。这种对IK1的作用有利于ICa的激活。因此，这些结果表明，氢化可的松的正性肌力作用至少部分是由对ICa的直接增强作用介导的。
