Forskolin stimulates swelling-induced chloride current, not cardiac cystic fibrosis transmembrane-conductance regulator current, in human cardiac myocytes.
Whole-cell patch clamp was used to look for cystic fibrosis transmembrane-conductance regulator (CFTR)-like chloride currents in calcium-tolerant human cardiac myocytes. Potassium-containing solutions were used initially. Steady state currents were measured with hyperpolarizing ramps (-16.25 mV/s). Peak net inward currents during voltage steps from -50 to +5 mV were used as an index of L-type calcium current. Isoproterenol (1 mumol/L) or forskolin (10 mumol/L) were used in attempts to evoke CFTR-like chloride current. No forskolin- or isoproterenol-induced steady state current was found in any of 17 atrial cells from seven patients in the absence of cell swelling. Every cell exhibited a large increase in net inward current in response to forskolin, suggesting that cAMP-dependent stimulation of L-type calcium current was present. Swelling with osmotic stress induced an outwardly rectifying steady state current with a reversal potential close to the chloride equilibrium potential. Once this current was activated, exposure to forskolin caused a further increase that subsided on washout (four of four cells, two patients). The atrial swelling-induced current was studied in more detail by using cesium-containing solutions. The current was determined to be a chloride current because the reversal potential was sensitive to changes in intracellular chloride and outward currents were blocked by 150 mumol/L DIDS. Ventricular cells were isolated from five failing human hearts. No CFTR-like current was found in any of 17 cells. In eight of eight ventricular cells, a swelling-induced current was found. The amplitude of the swelling-induced current was enhanced by forskolin.(ABSTRACT TRUNCATED AT 250 WORDS)
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Department of Surgery, Columbia University, New York, NY 10032, USA.
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D000200:Action Potentials; D000328:Adult; D000368:Aged; D018118:Chloride Channels / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003550:Cystic Fibrosis; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004594:Electrophysiology; D005260:Female; D006325:Heart Atria / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D006352:Heart Ventricles / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007249:Inflammation; D008297:Male; D008565:Membrane Proteins / Q000302:isolation & purification; D008875:Middle Aged; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D013268:Stimulation, Chemical
C505032:CFTR protein, human; D018118:Chloride Channels; D008565:Membrane Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases