Effect of insulin on potassium secretion in rabbit cortical collecting ducts
Furuya, H.; Tabei, K.; Muto, S.; Asano, Y.
American Journal of Physiology 262(1 Pt 2): F30-F35
1992
ISSN/ISBN: 0002-9513 PMID: 1733294 Document Number: 388443
Insulin is known to play an important role in the regulation of extrarenal K homeostasis. Previous clearance studies have shown that insulin decreases urinary K excretion, but the responsible nephron segments have not been identified. In this microperfusion study, in vitro, the effect of insulin on K transport in the cortical collecting duct (CCD), which is thought to be an important segment for regulation of the final urinary K excretion, was investigated. Basolateral insulin (10-6 M) significantly inhibited net K secretion by 20% (mean JK = -26.2 .+-. 4.2 peq.cntdot.mm-1.cntdot.min-1 for controls compared with -21.1 .+-. 3.4 with insulin, P < 0.001) and depolarized the transepithelial voltage (VT, from -14.6 .+-. 3.5 to -10.8 .+-. 3.5 mV, P < 0.005), recovery did not occur over 60 min. Insulin (10-11-10-5 M) depressed K secretion and depolarized the VT in a concentration-dependent manner. The half-maximal concentration was 5 .times. 10-10 M, which is within the physiological range of plasma insulin concentration. In tubules of deoxycorticosterone acetate-treated rabbits, insulin also produced a significant fall in K secretion (from -43.4 .+-. 7.5 to -36.1 .+-. 5.7 peq.cntdot.mm-1.cntdot.min-1, P < 0.05). Although luminal Ba (2 mM) decreased K secretion (from -14.4 .+-. 2.9 to -7.0 .+-. 1.7 peq.cntdot. mm-1.cntdot.mm-1), basolateral insulin (10-6 M) inhibited K secretion further (to -4.7 .+-. 1.3 peq.cntdot.mm-1.cntdot.min-1, P < 0.01). In contrast, luminal amiloride (1004 M) inhibited K secretion completely (from -13.3 .+-. 1.8 to -0.1 .+-. 0.5 peq.cntdot.mm-1.cntdot.min-1, P < 0.005), and basolateral insulin did not induced any further change in K transport (0.7 .+-. 1.0 peq.cntdot.mm-1.cntdot.min-1). Insulin also inhibited the unidirectional lumen-to-bath 22Na efflux (from 41.0 .+-. 5.9 to 30.8 .+-. 5.2 peq.cntdot.mm-1.cntdot.min-1, P < 0.025). These results demonstrate that inxulin directly inhibits K secretion and Na reabsorption in the rabbit CCD in vitro.