Absence of acetylcholine- and ionomycin-activated Cl- currents in submandibular cells of early postnatal rats.
Using the whole-cell patch-clamp technique, we investigated developmental changes in the expression of an acetylcholine- (Ach-) activated Cl- conductance in rat submandibular acinar cells. ACh induced an oscillatory inward current in cells isolated from animals older than 5 weeks, but not in animals less than 2-3 weeks of age. The current/voltage (I/V) relationship of the ACh-induced current was that of an outward rectifier, and the current was inhibited by intracellular BAPTA, a Ca2+ buffer, indicating the current was Ca2+ activated. The ACh-induced current was also blocked in the presence of DPC and SITS, two Cl- current inhibitors in other tissues. Ionomycin mimicked the effect of ACh but in a nonoscillatory fashion. The appearance of the ionomycin-induced currents was also age related, as the current was not observed to occur in animals less than 2-3 weeks old. Since both ACh and ionomycin significantly increase cytosolic [Ca2+] in the acinar cells of young animals, the correlation between the age dependence of the ACh-activated Cl- current and the ionomycin-activated Cl- current responses suggests that the lack of responsiveness observed in the young animals is due to the absence of Ca2+-activated Cl- channels, rather than to a deficiency of a cellular mediator.
Fatherazi
S
S
University of Washington, Department of Oral Biology, Box 357132, Seattle, WA 98195-7132, USA.
Izutsu
K T
KT
Martinez
J R
JR
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D016922:Cellular Senescence; D002712:Chlorides / Q000502:physiology*; D004553:Electric Conductivity; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013363:Submandibular Gland / Q000166:cytology / Q000378:metabolism*
D002712:Chlorides; D007476:Ionophores; D015759:Ionomycin; D000109:Acetylcholine