Acetylcholine-induced Ca++-dependent chloride current oscillations are mediated by inositol 1,4,5-trisphosphate in tracheal myocytes.
We demonstrated previously that acetylcholine (ACh) induces Ca++ oscillations in tracheal myocytes. These oscillations, as measured with fluo3-loaded cells and confocal microfluorimetry, correlated with Ca++-dependent Cl- current (Clca) oscillations measured by whole-cell voltage-clamp recording. In the current study, we investigated the role of inositol 1,4,5-trisphosphate (IP3) in ACh-induced oscillations in Ca++ and membrane currents. Both an IP3 receptor monoclonal antibody (5 micrograms/ml) and an IP3 receptor antagonist, heparin (5 mg/ml), directly introduced into the cells via the patch pipette, reduced or abolished oscillations in Clca induced by ACh. In addition, IP3 (1-100 microM) applied intracellularly, elicited concentration-dependent Clca oscillations that resembled those induced by ACh. Increasing external Ca++ concentration enhanced IP3-induced Clca oscillations, whereas verapamil (10 microM), a voltage-operated Ca++ channel blocker, attenuated IP3-induced Clca oscillations as well as both control and IP3-enhanced spontaneous transient outward currents. However, neither 5 microgram/ml IP3 receptor monoclonal antibody nor 5 mg/ml heparin altered the caffeine-induced transient Clca. Caffeine (10 mM) reversibly eliminated IP3-induced Clca oscillations as well as IP3-enhanced spontaneous transient outward currents, which indicates that caffeine releases Ca++ via a mechanism independent of the IP3 receptor. The findings are consistent with the hypothesis that ACh-induced Ca++ oscillations can arise and be sustained via IP3-induced Ca++ release pathways.
Liu
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Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, USA.
Farley
J M
JM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D018118:Chloride Channels / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D013552:Swine; D014132:Trachea / Q000378:metabolism*
D018118:Chloride Channels; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D000109:Acetylcholine; D002118:Calcium