Intracellular Ca2+ responses induced by acetylcholine in the submucosal nasal gland acinar cells in guinea pigs

Abstract

We examined intracellular Ca2+ responses of the nasal gland acinar cells to clarify cellular responses and molecular events with regard to the regulatory mechanism of the nasal secretion. The acinar cells of the serous gland in the nasal septum of guinea pigs were obtained by meticulous and selective dissection with minimal contamination by epithelial lining cells after collagenase treatment. The dispersed acini were incubated in the oxygenated solution supplemented with fura 2 acetoxymethyl ester, and the intracellular Ca2+ concentration ([Ca2+]i) was measured by fluorescence ratio imaging microscopy. The application of acetylcholine (ACh) to the cells induced an initially rapid increased [Ca2+]i followed by a sustained plateau. The increase in [Ca2+]i induced by ACh was concentration dependent, ranging between 10(-8) and 10(-4) M. The [Ca2+]i response was completely inhibited by atropine, further indicating the involvement of muscarinic cholinergic receptors. Removal of external Ca2+ with addition of EGTA resulted in a transient increase without a sustained phase, and the transient increase was abolished by the intracellular Ca2+ antagonist 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, indicating that this increase in [Ca2+]i was due to release from internal stores. The initial peak was not altered by changes in external pH, addition of adenosine 3',5'-cyclic monophosphate (cAMP), nor addition of phorbol 12-myristate 13-acetate (PMA) but was augmented by external K(+)-induced depolarization, suggesting that the transient increase was due to a changing in the binding affinity to inositol 1,4,5-trisphosphate. The sustained Ca2+ entry induced by ACh was inhibited by Ni2+, but not by nifedipine.(ABSTRACT TRUNCATED AT 250 WORDS)