Membrane crosstalk in secretory epithelial cells mediated by intracellular chloride concentration.
Fluid secretion by epithelial cells is modulated by agents which activate Cl- channels in the apical membrane. To sustain secretion, Cl- influx across the basolateral membrane must also be accelerated. To examine cellular mechanisms which couple Cl- efflux across the apical membrane to Na(+)-coupled Cl- entry across the basolateral membrane, we employed optical imaging techniques utilizing single rat salivary acinar cells. Na+ influx was negligible in resting cells, but was rapidly increased by carbachol due to activation of a Na(+)-H+ exchanger, Na(+)-K(+)-2Cl- cotransporter and likely a non-selective cation channel. Receptor stimulation was not necessary since elevation of [Ca2+]i by thapsigargin activated the Na+ transporters at equivalent rates. Cell acidification, activation of protein kinase C, and cell shrinkage, other events associated with the rise of [Ca2+]i, had little effect on Na+ transport in resting cells. Nevertheless, stimulation of cells in a medium which prevented normal Ca(2+)-induced cell shrinkage prevented activation of all three pathways. The block of the activation was not overcome by osmotic shrinkage, but was relieved when intracellular Cl- concentration ([Cl-]i) was allowed to fall, including conditions in which [Cl-]i fell in the absence of cell shrinkage. Activation of a Na(+)-H+ exchanger, Na(+)-K(+)-2Cl- cotransporter, and non-selective cation channel therefore exhibit a requirement for agonist-induced fall in [Cl-]i. Low [Cl-]i may create a permissive environment for Ca(2+)-dependent activation of multiple Na+ transport pathways, providing for crosstalk which coordinates transport activities of apical and basolateral membranes in secretory epithelial cells.
Robertson
M A
MA
Division of Cell Biology, Hospital for Sick Children, Ontario, Canada.
Foskett
J K
JK
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology*; D002712:Chlorides / Q000494:pharmacology*; D004848:Epithelium / Q000502:physiology; D017136:Ion Transport / Q000502:physiology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012469:Salivary Glands; D012964:Sodium / Q000494:pharmacology
D002712:Chlorides; D002217:Carbachol; D012964:Sodium; D002118:Calcium