Ja. Murray et al., NITRIC-OXIDE MODULATES A CALCIUM-ACTIVATED POTASSIUM CURRENT IN MUSCLE-CELLS FROM OPOSSUM ESOPHAGUS, American journal of physiology: Gastrointestinal and liver physiology, 32(4), 1995, pp. 606-612
Nitric oxide mediates nerve-induced hyperpolarization of circular smoo
th muscle of the esophagus. Two mechanisms are proposed to explain thi
s hyperpolarization: an increase in K+ current or a decrease in Cl- cu
rrent. These studies test the hypothesis that nitric oxide increases a
K+ current in esophageal smooth muscle. Three outward K+ currents are
present in circular smooth muscle cells from the opossum esophagus. O
ne current is a Ca2+- activated K+ current (I-K Ca 2+. This current is
inhibited by charybdotoxin. Whole cell currents were recorded from is
olated opossum esophageal smooth muscle cells using the whole cell pat
ch-clamp technique. These studies showed that I-K Ca 2+ is activated a
t potentials more positive than -30 mV. Bath application of S-nitroso-
L-cysteine increased I-K Ca 2+ by 50% above control levels throughout
the entire activation range of potentials. The enhanced current was re
versible on washout. Either charybdotoxin, an inhibitor of I-K Ca 2+,
or (R)-p-8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphoroth
ioate, an inhibitor of protein kinase G, antagonized the increase in o
utward current induced by S-nitroso-L-cysteine. These data suggest tha
t nitric oxide activates I-K Ca 2+ via the guanosine 3',5'-cyclic mono
phosphate-protein kinase G signal transduction pathway.