Nitric oxide suppresses a Ca(2+)-stimulated Cl- current in smooth muscle cells of opossum esophagus.
Nitric oxide (NO) hyperpolarizes visceral smooth muscles. Using the patch-clamp technique, we investigated the possibility that NO-mediated hyperpolarization in the circular muscle of opossum esophagus results from the suppression of a Ca(2+)-stimulated Cl- current. Smooth muscle cells were dissociated from the circular layer and bathed in high-K+ Ca(2+)-EGTA-buffered solution. Macroscopic ramp currents were recorded from cell-attached patches. Contaminating K(+)-channel currents were blocked with tetrapentylammonium chloride (200 microM) added to all solutions. Raising bath Ca2+ concentration above 150 nM in the presence of A-23187 (10 microM) activated a leak current (IL-Ca) with an EC50 of 1.2 microM at -100 mV. The reversal potential (Erev) of IL-Ca (-8.5 +/- 1.8 mV, n = 8) was significantly different (P < 0.05) from Erev of the background current (+4.2 +/- 1.2 mV, n = 8). Equimolar substitution of 135 mM Cl- in the pipette solution with gluconate significantly shifted Erev of IL-Ca to +16.6 +/- 3.4 mV (n = 4) (P < 0.05 compared with background), whereas replacement of total Na+ with Tris+ suppressed IL-Ca but did not affect Erev (-15 +/- 3 mV, n = 3; P > 0.05). IL-Ca was inhibited by DIDS (500 microM). Diethylenetriamine-NO adduct (200 microM), a NO donor, and 8-bromo-cGMP (200 microM) suppressed IL-Ca by 59 +/- 15% (n = 5) and 62 +/- 21% (n = 4) at -100 mV, respectively. We conclude that in opossum esophageal smooth muscle NO-mediated hyperpolarization may be produced by suppression of a Ca(2+)-stimulated Cl(-)-permeable conductance via formation of cGMP.
Zhang
Y
Y
Center for Swallowing and Motility Disorders, Brockton/West Roxbury Veterans Affairs Medical Center 02132, USA.
Vogalis
F
F
Goyal
R K
RK
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000502:physiology*; D004553:Electric Conductivity; D004947:Esophagus / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology*; D009893:Opossums; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000494:pharmacology; D014226:Triazenes / Q000494:pharmacology
C105351:1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene; D002712:Chlorides; D014226:Triazenes; D009569:Nitric Oxide; D012964:Sodium; D002118:Calcium