Frequency modulation of acetylcholine-induced oscillations in Ca++ and Ca(++)-activated Cl- current by cAMP in tracheal smooth muscle.
The effects of adenosine 3':5'-cyclic monophosphate (cAMP) on acetylcholine (ACh)-induced oscillations in intracellular calcium concentration ([Ca++]i) and Ca(++)-activated Cl- current (ClCa current) were determined in isolated tracheal smooth muscle cells. Whole-cell current was measured in individual smooth muscle cells with patch clamp methodology. At a holding potential of -80 mV, ACh (0.1 microM) elicits base line-separated oscillations in ClCa current which correlate with oscillations in [Ca++]i. The addition of the beta adrenoceptor agonist isoproterenol (ISO) (10 nM to 1 microM) in the continued presence of ACh caused a concentration-dependent decrease in the frequency of the oscillations in ClCa current with significant reductions in oscillation frequency of 21.4 and 81.5% in the presence of 0.01 and 0.1 microM ISO, respectively (P < .05). This effect was mimicked by both forskolin (FSK) (3 microM) and 3-isobutyl-1-methylxanthine (IBMX) (30 microM). ISO and forskolin also inhibited ACh-induced oscillations in [Ca++]i measured by confocal fluorescence microscopy in non-voltage-clamped cells loaded with the Ca(++)-sensitive dye, fluo3. The inhibition of ACh-induced oscillations in ClCa current by ISO was partially reversed by increasing extracellular Ca++. These data are consistent with previous observations that the frequency of ACh-induced oscillations in [Ca++]i and ClCa current is dependent on the concentration of extracellular Ca++ and the influx of Ca++ through a verapamil-sensitive pathway. Moreover, these results lend support to the hypothesis that beta adrenoceptors inhibit the ACh-induced increase in [Ca++]i through a cAMP-dependent mechanism that inhibits Ca++ influx and in independent of changes in membrane potential.
Nuttle
L C
LC
Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, USA.
Farley
J M
JM
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018118:Chloride Channels / Q000187:drug effects*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects; D013552:Swine; D014132:Trachea / Q000187:drug effects* / Q000378:metabolism
D018118:Chloride Channels; D015221:Potassium Channels; D005576:Colforsin; D000242:Cyclic AMP; D007545:Isoproterenol; D000109:Acetylcholine; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine