A novel Cl- conductance in cultured chick cardiac myocytes: role of intracellular Ca2+ and cAMP.
Cl- conductance in cultured embryonic chick cardiac myocytes was characterized using whole-cell patch clamp techniques. Following elimination of cation currents in Na(+)- and K(+)-free internal and external solutions, the basal whole-cell current was predominantly a Cl- current. Cl(-)-sensitive current (ICl) was defined as the difference between the whole-cell currents recorded in normal and low [Cl-]o when measured in the same cell. The whole-cell current in the absence or presence of 10 microM cAMP was time independent, displayed outward rectification with the pipette [Cl-] < 40 mM, and was not saturated with a physiological Cl- gradient. The Cl- current was also activated by 1 microM forskolin and inhibited by 0.3 mM anthracene-9-carboxylic acid (9-AC). Forskolin was less effective than cAMP (internal dialysis) in activating the Cl- current. The cAMP- or forskolin-activated and basal Cl- current were reasonably fit by the Goldman-Hodgkin-Katz equation. The calculated PCl in the presence of cAMP was increased by five- to sixfold over the basal level. In the presence of 5 mM EGTA to decrease free [Ca2+]i, the whole-cell current could not be stimulated by cAMP, forskolin or IBMX (0.1 mM). These data suggest that cultured chick cardiac myocytes have a low basal Cl- conductance, which, as in some mammalian cardiac ventricular myocytes, can be activated by cAMP. However, this study shows that the activation process requires physiological free [Ca2+]i.
Department of Medicine, University of Arkansas for Medical Sciences, Little Rock 72205.
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S
Liu
J R
JR
Stimers
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M
Lieberman
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002264:Carboxylic Acids / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology / Q000502:physiology*; D006321:Heart / Q000196:embryology; D017136:Ion Transport; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques
D002264:Carboxylic Acids; D018118:Chloride Channels; D005576:Colforsin; D000242:Cyclic AMP; D002118:Calcium