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

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