Regulation of K[sup +] transport in the rat distal colon via angiotensin II subtype receptors and K[sup +]-pathways.

The role of angiotensin subtype-1 (AT[sub 1]) and -2 (AT[sub 2]) receptors in mediating the effects of angiotensin II (ANG II) on several K[sup +] transporters was studied in rat distal colon using an Ussing chamber. Angiotensin II induced K[sup +] secretion at two different doses. Secretion occurred at 10[sup -8] and 10[sup -4, sub M], as a result of an increase in serosal-to-mucosal flux (J[sub s-m]). The ANG II-induced stimulation of J[sub s-m] at a low dose (10[sup -8] M) was abolished by PD123319 while losartan did not alter the low-dose ANG II-dependent increase in J[sub s-m]. In contrast, the increase in J[sub s-m] induced by a high-dose of ANG II (10[sup -4, sub M]) was blocked by losartan, whereas PD123319 partially reduced the stimulatory effect. In the presence of both blockers, high-dose ANG II induced an inhibition of basal J[sub s-m]. Low-dose ANG II activated the barium-sensitive K[sup +] channels, whereas the Na[sup +], K[sup +], 2Cl[sup -] cotransporter and the Na[sup +], K[sup +]-ATPase pump were unchanged. At the high dose, ANG II activated the barium-sensitive K[sup +] channels and the Na[sup +], K[sup +], 2Cl[sup -] cotransporter and inhibited the Na[sup +], K[sup +]-ATPase pump. These data indicate that ANG II stimulates serosal-to-mucosal K[sup +] flux in the rat distal colon at high and low doses via different receptors and K[sup +] transporters. [ABSTRACT FROM AUTHOR]