Secretory state regulates Zn2+ transport in gastric parietal cell of the rabbit

摘要

Secretory compartments of neurons, endocrine cells, and exocrine glands are acidic and contain high levels of labile Zn²⁺. Previously, we reported evidence that acidity is regulated, in part, by the content of Zn²⁺ in the secretory [i.e., tubulovesicle (TV)] compartment of the acid-secreting gastric parietal cell. Here we report studies focusing on the mechanisms of Zn²⁺ transport by the TV compartment in the mammalian (rabbit) gastric parietal cell. Uptake of Zn²⁺ by isolated TV structures was monitored with a novel application of the fluorescent Zn²⁺ reporter N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ). Uptake was suppressed by removal of external ATP or blockade of H⁺-K⁺-ATPase that mediates luminal acid secretion. Uptake was diminished with dissipation of the proton gradient across the TV membrane, suggesting Zn²⁺/H⁺ antiport as the connection between Zn²⁺ uptake and acidity in the TV lumen. In isolated gastric glands loaded with the reporter fluozin-3, inhibition of H⁺-K⁺-ATPase arrested the flow of Zn²⁺ from the cytoplasm to the TV compartment and secretory stimulation with forskolin enhanced vectorial movement of cytoplasmic Zn²⁺ into the tubulovesicle/lumen (TV/L) compartment. Our findings suggest that Zn²⁺ accumulation in the TV/L compartment is physiologically coupled to secretion of acid. These findings offer novel insight into mechanisms regulating Zn²⁺ homeostasis in the gastric parietal cell and potentially other cells in which acidic subcellular compartments serve signature functional roles.