Myosin IIB and F-actin control apical vacuolar morphology and histamine-induced trafficking of H-K-ATPase-containing tubulovesicles in gastric parietal cells

Abstract

Selective inhibitors of myosin or actin function and confocal microscopy were used to test the role of an actomyosin complex in controlling morphology, trafficking, and fusion of tubulovesicles (TV) containing H-K-ATPase with the apical secretory canaliculus (ASC) of primary-cultured rabbit gastric parietal cells. In resting cells, myosin IIB and IIC, ezrin, and F-actin were associated with ASC, whereas H-K-ATPase localized to intracellular TV. Histamine caused fusion of TV with ASC and subsequent expansion resulting from HCl and water secretion; F-actin and ezrin remained associated with ASC whereas myosin IIB and IIC appeared to dissociate from ASC and relocalize to the cytoplasm. ML-7 (inhibits myosin light chain kinase) caused ASC of resting cells to collapse and most myosin IIB, F-actin, and ezrin to dissociate from ASC. TV were unaffected by ML-7. Jasplakinolide (stabilizes F-actin) caused ASC to develop large blebs to which actin, myosin II, and ezrin, as well as tubulin, were prominently localized. When added prior to stimulation, ML-7 and jasplakinolide prevented normal histamine-stimulated transformations of ASC/TV and the cytoskeleton, but they did not affect cells that had been previously stimulated with histamine. These results indicate that dynamic pools of actomyosin are required for maintenance of ASC structure in resting cells and for trafficking of TV to ASC during histamine stimulation. However, the dynamic pools of actomyosin are not required once the histamine-stimulated transformation of TV/ASC and cytoskeleton has occurred. These results also show that vesicle trafficking in parietal cells shares mechanisms with similar processes in renal collecting duct cells, neuronal synapses, and skeletal muscle.

Gastric secretion

“…These morphological changes involve changes in the actin cytoskeleton located directly beneath the apical microvilli. Using inhibitors of myosin or actin function and confocal microscopy, it was shown, in cultured rabbit parietal cells, that nonmuscle myosin IIB and F-actin play an important role in the translocation and fusion of H-K-ATPase-containing tubulovesicles with the apical microvilli during stimulation with histamine [47]. Other proteins implicated in the membrane trafficking include ezrin, Rab GTPases, and soluble N-ethylmaleimide-sensitive factor attachment protein receptors [48].…”

Motor neuron boutons remodel through membrane blebbing

“…Altogether, our results suggest that bleb size seems to be determined by a balance between the initial growth rate (the rate of volume expansion due to cytoplasm flow) and the time needed for actin to repolymerize at the bleb membrane, which can be changed according with prevailing local actin dynamics. While JAS has been reported to either cause or block blebbing 62,63 , one hypothesis is that in cases where the flow rate of cytoplasm is insufficient to outpace local actin polymerization it could result in small or no blebs, whereas cases where actin filaments are highly stabilized would also restrict bleb formation. Supporting this hypothesis smaller boutons appear frequently together or in nearby regions, suggesting that they were formed during the same event, sequentially.…”

Gastric Parietal Cell Physiology and Helicobacter pylori–Induced Disease

“…64 Dynamic pools of actomyosin and F-actin are required to maintain apical membrane structures in resting cells and for trafficking of tubulovesicles to the apical plasma membranes during histamine stimulation. 65…”