Rechkemmer G, Halm D R
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
Proc Natl Acad Sci U S A. 1989 Jan;86(1):397-401. doi: 10.1073/pnas.86.1.397.
K transport across guinea pig (Cavia porcellus) distal colon was measured in vitro using isotopically determined unidirectional fluxes. Aldosterone stimulated electrogenic Na absorption, as measured by amiloride-sensitive short-circuit current (Isc), and reduced net K absorption from +2.5 +/- 0.2 microEq/cm2 per hr to +0.8 +/- 0.3 microEq/cm2 per hr (mean +/- SEM). Amiloride addition to the mucosal solution did not enhance net K absorption, as expected if inhibiting active Na absorption would reduce active K secretion as in the distal nephron. The amiloride-insensitive Isc was -1.0 +/- 0.2 microEq/cm2 per hr (mean +/- SEM) and was inhibited by mucosal addition of Ba, a K channel blocker. Addition of bumetanide to the serosal solution also inhibited this negative Isc, and K transport returned to the control level of net absorption. Thus, the amiloride-insensitive, negative Isc is consistent with active K secretion stimulated by aldosterone. This stimulation of an active K secretory pathway by aldosterone occurred without altering the active K absorption pathway that also is present. These results indicate that the aldosterone-stimulated K secretory pathway operates independently of the amiloride-sensitive Na absorption pathway, which also is stimulated by aldosterone.
利用同位素测定的单向通量，在体外测量了豚鼠（豚鼠）远端结肠的钾转运。醛固酮刺激了由氨氯地平敏感短路电流（Isc）测量的电中性钠吸收，并使净钾吸收从每小时+2.5±0.2微当量/平方厘米降至每小时+0.8±0.3微当量/平方厘米（平均值±标准误）。如预期的那样，如果抑制主动钠吸收会减少主动钾分泌，就像在远端肾单位中那样，那么向黏膜溶液中添加氨氯地平并不会增强净钾吸收。氨氯地平不敏感的Isc为每小时-1.0±0.2微当量/平方厘米（平均值±标准误），并且被黏膜添加钾通道阻滞剂钡所抑制。向浆膜溶液中添加布美他尼也抑制了这种负Isc，钾转运恢复到净吸收的对照水平。因此，氨氯地平不敏感的负Isc与醛固酮刺激的主动钾分泌一致。醛固酮对主动钾分泌途径的这种刺激在不改变同样存在的主动钾吸收途径的情况下发生。这些结果表明，醛固酮刺激的钾分泌途径独立于氨氯地平敏感的钠吸收途径发挥作用，而后者也受到醛固酮的刺激。
