Caffeine- and carbachol-induced Cl- and cation currents in single opossum esophageal circular muscle cells.
Cl- and cation currents may play important roles in esophageal smooth muscle membrane potential changes and contraction. We studied Ca2+ release-activated cell-shortening and membrane currents in single cells freshly dispersed from the circular muscle of the opossum esophagus using the standard patch-clamp whole cell recording method. Caffeine (10-20 microM) and carbachol (10-100 microM) shortened the single smooth muscle cells by releasing intracellular Ca2+. At a holding potential of 0 mV, spontaneous transient outward currents STOCs, representing spontaneous Ca(2+)-activated K+ currents) were recorded. Caffeine, carbachol, or ionomycin evoked large outward currents (up to 1,650 pA) and subsequently abolished STOCs. At a holding potential of -50 mV in K(+)-containing solutions, an outward current in response to the agonists was observed; in some cells, the outward current followed an inward current. In K(+)-free solutions, the agonists induced only an inward current whose reversal potential was shifted by alteration of the anion gradient but not by that of the cation. With a low-Cl- pipette solution (Cl- substituted by glucuronate or glutamate), the inward currents were dependent mainly on the external cation gradient. This cation channel was permeable to Ba2+. Inclusion of 10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the pipette solution abolished all these currents. These data suggest that in the opossum esophageal circular muscle 1) Ca2+ released from the intracellular stores by caffeine and carbachol is sufficient to induce single smooth muscle cell contraction and 2) the caffeine-, carbachol-, and ionomycin-induced membrane currents consist of Ca(2+)-activated K+, Cl-, and cation conductances.
Wang
Q
Q
Center for Swallowing and Motility Disorders, Beth Israel Hospital, Harvard Medical School, Boston 02215, USA.
Akbarali
H I
HI
Hatakeyama
N
N
Goyal
R K
RK
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D002412:Cations / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D004947:Esophagus / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009893:Opossums; D018408:Patch-Clamp Techniques
D002412:Cations; D002712:Chlorides; D002110:Caffeine; D015759:Ionomycin; D002217:Carbachol; D002118:Calcium