Gómez, Luis Alberto

ABSTRACT Bacteria that produce heat‐stable enterotoxins (STs), a leading cause of secretory diarrhea, are a major cause of morbidity and mortality worldwide. ST stimulates guanylyl cyclase C (GCC) and accumulation of intracellular cyclic GMP ([cGMP] i ), which opens the cystic fibrosis transmembrane conductance regulator (CFTR)‐related chloride channel, triggering intestinal secretion. Although the signaling cascade mediating ST‐induced diarrhea is well characterized, antisecretory therapy targeting this pathway has not been developed. 2‐ChloroATP (2ClATP) and its cell‐permeant precursor, 2‐chloroadenosine (2ClAdo), disrupt ST‐dependent signaling in intestinal cells. However, whether the ability to disrupt guanylyl cyclase signaling translates into effective antisecretory therapy remains untested. In this study, the efficacy of 2ClAdo to prevent ST‐induced water secretion by human intestinal cells was examined. In Caco‐2 human intestinal cells, ST increased [cGMP] i , induced a chloride current, and stimulated net basolateral‐to‐apical water secretion. This effect on chloride current and water secretion was mimicked by the cell‐permeant analog of cGMP, 8‐bromo‐cGMP. Treatment of Caco‐2 cells with 2ClAdo prevented ST‐induced increases in [cGMP] i , chloride current and water secretion. Inhibition of the downstream consequences of ST‐GCC interaction reflects proximal disruption of cGMP production because 8‐bromo‐cGMP stimulated chloride current and water secretion in 2ClAdo‐treated cells. Thus, this study demonstrates that disruption of guanylyl cyclase signaling is an effective strategy for antisecretory therapy and provides the basis for developing mechanism‐based treatments for enterotoxigenic diarrhea.—Zhang, W., Mannan, I., Schulz, S., Parkinson, S. J., Alekseev, A. E., Gomez, L. A., Terzic, A., Waldman, S. A. Interruption of transmembrane signaling as a novel antisecretory strategy to treat enterotoxigenic diarrhea. FASEB J. 13, 913–922 (1999)

The efficacy with which sulfonylurea drugs inhibit cardiac ATP-sensitive K+ (KATP) channels is reduced during metabolic compromise and cellular contracture. Disruption of the actin microfilament network, which occurs under similar conditions, reduces the sensitivity of the channel toward intracellular ATP. To investigate whether a disrupter of actin microfilaments could also affect the responsiveness of the KATP channel to sulfonylurea drugs, single-channel currents were measured in the inside-out configuration of excised patches from guinea pig ventricular myocytes. Treatment of the internal side of patches with deoxyribonuclease (DNase) I (100 micrograms/ml), which forms complexes with G actin and prevents actin filament formation, antagonized sulfonylurea-induced inhibition of KATP channels that was coupled with a loss of sensitivity to ATP. The apparent dissociation constant and Hill coefficient for the inhibitory effect of glyburide, a prototype sulfonylurea, on KATP-channel opening were, respectively, 0.13 microM and 0.95 before and 2.7 microM and 0.98 after DNase treatment. DNase did not alter intraburst kinetic properties of the channel. When DNase was denatured or coincubated with purified actin (200 micrograms/ml), it no longer decreased glyburide-induced channel inhibition. This suggests that sulfonylurea-inhibitory gating of cardiac KATP channels may also be regulated through a mechanism involving subsarcolemmal actin microfilament networks.