Mq. Lin et al., HEAT-STABLE TOXIN FROM ESCHERICHIA-COLI ACTIVATES CHLORIDE CURRENT VIA CGMP-DEPENDENT PROTEIN-KINASE, Cellular physiology and biochemistry, 5(1), 1995, pp. 23-32
Heat-stable toxin (STa) increases cyclic GMP (cGMP) in isolated intest
inal cells and in T84 cells, a colonic secretory cell line. Whole-cell
current recordings from patch clamp experiments show identical proper
ties for currents activated by either STa or the cystic fibrosis trans
membrane conductance regulator (CFTR) channel. STa-activated currents
display a linear current-voltage relationship and a relative permeabil
ity sequence of Br > Cl > I. STa or 8-Br-cGMP-activated currents remai
n when 20 mu M Walsh inhibitor, a blocker of protein kinase A (PKA), i
s added in the pipette, suggesting that cGMP-dependent protein kinase
(PKG) activates the currents. Intracellular addition of Rp-8-Br-cGMP,
an agent that activates PKGII and inhibits PKGI and PKA, causes induct
ion of a chloride conductance identical to that stimulated by STa. We
conclude that STa activates CFTR by phosphorylation with cGMP-dependen
t protein kinase.