NHE3-dependent cytoplasmic alkalinization is triggered by Na+-glucose cotransport in intestinal epithelia

Cytoplasmic pH (pH(i)) was evaluated during Na+-glucose cotransport in Caco -2 intestinal epithelial cell monolayers. The pH(i) increased by 0.069 +/- 0.002 within 150 s after initiation of Na+-glucose cotransport. This increa se occurred in parallel with glucose uptake and required expression of the intestinal Na+-glucose cotransporter SGLT1. S-3226, a preferential inhibito r of Na+/H+ exchanger (NHE) isoform 3 (NHE3), prevented cytoplasmic alkalin ization after initiation of Na+-glucose cotransport with an ED50 of 0.35 mu M, consistent with inhibition of NHE3, but not NHE1 or NHE2. In contrast, H OE-694, a poor NHE3 inhibitor, failed to significantly inhibit pH(i) increa ses at <500 <mu>M. Na+-glucose cotransport was also associated with activat ion of p38 mitogen-activated protein (MAP) kinase, and the p38 MAP kinase i nhibitors PD-169316 and SB-202190 prevented pH(i) increases by 100 +/- 0.1 and 86 +/- 0.1%, respectively. Conversely, activation of p38 MAP kinase wit h anisomycin induced NHE3-dependent cytoplasmic alkalinization in the absen ce of Na+-glucose cotransport. These data show that NHE3-dependent cytoplas mic alkalinization occurs after initiation of SGLT1-mediated Na+-glucose co transport and that the mechanism of this NHE3 activation requires p38 MAP k inase activity. This coordinated regulation of glucose (SGLT1) and Na+ (NHE 3) absorptive processes may represent a functional activation of absorptive enterocytes by luminal nutrients.