Chromaffin cells as a neuron model

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A large fraction of rat adrenal chromaffin cells (about 60%) shows spontaneous [Ca^<2+>]_c oscillations and spontaneous action potentials. GABA (gamma-aminobutyricacid) inhibited the spontaneous [Ca^<2+>]_c oscillations in a reversible manner. The effect of GABA was mimicked by the GABA_A receptor, which may increase chloride ion conductance (Kanno). Palytoxin is much more proper than gramicidin for in vivo calibration of SBFI to measure intracellular Na^+ concentration ([Na^+]i) in SBFI-treated cultured porcine adrenal chromaffin cells (Nakazato). Yanagihara et al. isolated a new endogenoussubstrate for Ca^<2+>/calmodulin-dependent protein kinase II from bovine adrenal medullary cells. Protein sequencing and immunoblotting revealed that the new substrate may be chromogranin A (Yanagihara). Protein kinase C (PKC) may be involved in a signal transductionactivated by histamine, which may down-regulate receptor/G-protein system in rat adrenal chromaffincells (Warashina). Kumakura et al. have studied the effects of antibodies against C2A and C2B domains ofsynaptotagmin and the effects of inositol high-polyphosphate series (IHPS) on Ca^<2+>-evoked catecholamine (CA) release from digitonin-permeabilized adrenal chromaffin cells. IHPS binding to the C2B domain might keep the docked or primed vesicles away from spontaneous fusion at resting level of intracellular Ca^<2+> (Kumakura). By using a confocal laser microscope and an anionic dye (HPTS) added to extracellularmedium, endocytosis associated with exocytosis was studied in cultured bovine adrenal chromaffin cells. Alarge vacuolar space often formed immediately after an exocytotic response of a single granule was confirmed to be an invagination of the plasm membrane (Terakawa).