FIGURE 6.

Morphological changes in parietal cells that accompany gastric acid secretion. This graphic derived from the hand-drawn figure from John Forte depicts the morphological stages in the course of parietal cell stimulation (105). In the resting state, parietal cells contain many mitochondria, numerous membrane tubulovesicles, and collapsed intracellular canaliculi. Upon stimulation, exocytosis results in fusion of the H⁺-K⁺-ATPase rich tubulovesicles with the intracellular canaliculus, resulting in an expanded secretory canalicular membrane and the elongation of apical microvilli-like structures. Following stimulation, endocytosis occurs to retrieve the H⁺-K⁺-ATPase and recycle the membrane to tubulovesicles in the resting state and to prepare for the next stimulus and return.