Local and global calcium signals and fluid and electrolyte secretion in mouse submandibular acinar cells.
Polarized Ca(2+) signals that originate at and spread from the apical pole have been shown to occur in acinar cells from lacrimal, parotid, and pancreatic glands. However, "local" Ca(2+) signals, that are restricted to the apical pole of the cell, have been previously demonstrated only in pancreatic acinar cells in which the primary function of the Ca(2+) signal is to regulate exocytosis. We show that submandibular acinar cells, in which the primary function of the Ca(2+) signal is to drive fluid and electrolyte secretion, are capable of both Ca(2+) waves and local Ca(2+) signals. The generally accepted model for fluid and electrolyte secretion requires simultaneous Ca(2+)-activation of basally located K(+) channels and apically located Cl(-) channels. Whereas a propagated cell-wide Ca(2+) signal is clearly consistent with this model, a local Ca(2+) signal is not, because there is no increase in intracellular Ca(2+) concentration at the basal pole of the cell. Our data provide the first direct demonstration, in submandibular acinar cells, of the apical and basal location of the Cl(-) and K(+) channels, respectively, and confirm that local Ca(2+) signals do not Ca(2+)-activate K(+) channels. We reevaluate the model for fluid and electrolyte secretion and demonstrate that Ca(2+)-activation of the Cl(-) channels is sufficient to voltage-activate the K(+) channels and thus demonstrate that local Ca(2+) signals are sufficient to support fluid secretion.
Harmer
A R
AR
Clinical Dental Sciences, The University of Liverpool, Liverpool L69 3GN, UK.
Smith
P M
PM
Gallacher
D V
DV
D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D018118:Chloride Channels / Q000502:physiology*; D003592:Cytophotometry; D005089:Exocytosis; D008297:Male; D051379:Mice; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D015398:Signal Transduction; D013363:Submandibular Gland / Q000166:cytology / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D018118:Chloride Channels; D015221:Potassium Channels; D002118:Calcium