| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1999: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1998: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
Diuretics augment KィイD1+ィエD1 which sometimes cause hypokalemia, because the diuretic-induced increase of luminal flow enhances flow-dependent KィイD1+ィエD1 secretion in distal nephron. In order to clarify the mechanism of flow-dependent KィイD1+ィエD1 secretion, Single channel currents were recorded from the luminal membrane of an everted rabbit connecting tubule with patch clamp technique. In cell-attached patch clamp studies, CaィイD12+ィエD1-activated maxi KィイD1+ィエD1 channels (280pS) found in this membrane showed little open probability compared with that of small conductance KィイD1+ィエD1 channels (35pS), although they were activated by stretching path membrane. The maxi KィイD1+ィエD1 channels were not totally blocked with 1μM charybdotoxin, but not with 33μM arachidonic acid. The small conductance KィイD1+ィエD1 channels, vice versa. Luminal KィイD1+ィエD1 conductance in the connecting tubule perfused, in vitro, was estimated from the deflection of transepithelial voltage (ΔVィイD1tィエD1), when luminal KィイD1+ィエD1 concentration was increased from 5 to 15mEq, by adding 10mM K gluconate. The luminal KィイD1+ィエD1 was increased flow-dependently and was blocked with luminally applied 1μM charybdotoxin. The 33mM arachidonic acid applied into lumen showed no effect on the luminal KィイD1+ィエD1 conductance estimated above. These observations suggest that the activation of maxi KィイD1+ィエD1 channels coupled with stretch-activation of Ca-permeable nonselective cation channels found in the same membrane play a dominat role in flow-dependent KィイD1+ィエD1secretion. It is likely that an increased luminal flow induced by an application of diuretic stimulates the coupling between stretch-activated cation channels and maxi KィイD1+ィエD1 and that KィイD1+ィエD1 secreted via the maxi KィイD1+ィエD1 in the rabbit connecting tubules.
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