Figure 3.
Effect of HNMPA-(AM)3 on insulin-stimulated Na+ absorption and concentration–response relationships for insulin and IGF-I. (A) Representative tracing showing that pretreatment with 25 μM HNMPA-(AM)3, an inhibitor of insulin receptor tyrosine kinase activity, added to the basolateral solution for 30 min abolished the increase in Isc produced by basolateral addition of 850 nM insulin. (B) Concentration–response relationships showing an acute increase in Isc after treatment with various concentrations of insulin or IGF-I added to the basolateral solution of monolayers. Experiments were performed using cells maintained in serum-free media for 4 d. The EC50 value was 12 nM for insulin (○) and 2.5 nM for IGF-I (•; n = at least 5, N = 3 for each concentration).