Simultaneous measurement and imaging of intracellular Ca2+ and H+ transport in isolated rabbit gastric glands

Activation of H + secretion in the intracellular canaliculi of parietal cells occurs on an unknown time scale with ill-defined kinetics for the coupling of H + secretion and the elevation of intracellular calcium ([Ca 2+ ] i ) stimulated by secretagogues. We developed a method to determine H + secretion in isolated rabbit gastric glands with spatio-temporal resolution, using the fluorescent indicator Lysosensor Yellow-Blue (LYB). Glands accumulated the dye exclusively in the intracellular canaliculi of parietal cells and the gland lumen. Dye fluorescence in the acid spaces of the glands increased upon stimulation of acid secretion by carbachol, histamine and forskolin. Simultaneous fluorescence measurements of acid secretion and [Ca 2+ ] i at 1 s resolution were made by joint loading of LYB and Fluo-3. Carbachol-stimulated H + secretion was detected in the gland lumen as early as 3 s after the onset of the [Ca 2+ ] i spike. H + accumulation appeared to be transient and paralleled the release component of the [Ca 2+ ] i spike. Short and repetitive stimulations with carbachol elicited repetitive responses in [Ca 2+ ] i and H + secretion. Histamine or forskolin stimulated H + secretion with a delayed onset (around 2 min) and a sustained response. Acid secretion was temporally unrelated to the oscillatory Ca 2+ responses. The striking difference in the kinetics of activation of H + secretion by cholinergic and cAMP-dependent secretagogues indicates that two distinct mechanisms are operating in the final stimulation of the pump, in spite of both eliciting a [Ca 2+ ] i response.