Mechanisms of secretion-associated shrinkage and volume recovery in cultured rabbit parietal cells

Abstract

We have previously shown that stimulation of acid secretion in parietal cells causes rapid initial cell shrinkage, followed by Na(+)/H(+) exchange-mediated regulatory volume increase (RVI). The factors leading to the initial cell shrinkage are unknown. We therefore monitored volume changes in cultured rabbit parietal cells by confocal measurement of the cytoplasmic calcein concentration. Although blocking the presumably apically located K(+) channel KCNQ1 with chromanol 293b reduced both the forskolin- and carbachol-induced cell shrinkage, inhibition of Ca(2+)-sensitive K(+) channels with charybdotoxin strongly inhibited the cell volume decrease after carbachol, but not after forskolin stimulation. The cell shrinkage induced by both secretagogues was partially inhibited by blocking H(+)-K(+)-ATPase with SCH28080 and completely absent after incubation with NPPB, which inhibits parietal cell anion conductances involved in acid secretion. The subsequent RVI was strongly inhibited with the Na(+)/H(+) exchanger 1 (NHE1)-specific concentration of HOE642 and completely by 500 muM dimethyl-amiloride (DMA), which also inhibits NHE4. None of the above substances induced volume changes under baseline conditions. Our results indicate that cell volume decrease associated with acid secretion is dependent on the activation of K(+) and Cl(-) channels by the respective secretagogues. K(+), Cl(-), and water secretion into the secretory canaliculi is thus one likely mechanism of stimulation-associated cell shrinkage in cultured parietal cells. The observed RVI is predominantly mediated by NHE1.

Enhanced insulin sensitivity of gene-targeted mice lacking functional KCNQ1

“…Decreased K ϩ channel activity leads to depolarization, which in turn decreases the electrical driving force for electrogenic bicarbonate exit and thus favors cellular HCO 3 Ϫ retention and intracellular alkalinisation (1,28). Intracellular alkalinisation, in turn, stimulates flux through glycolysis and thus enhances glucose utilization (1,4,37,39).…”

“…KCNQ1 further participates in cell volume regulation (3,18,25,26,53). In turn, cell volume has been shown to be a critical element in the regulation of metabolism and signaling of insulin (19 -21, 44).…”

Computer modeling of gastric parietal cell: significance of canalicular space, gland lumen, and variable canalicular [K+]

“…Parietal cells have been reported to be ϳ14% of mucosal volume in humans (1) and we approximated aggregate parietal cell cytosolic volume as 0.01 cm 3 /cm 2 mucosa, fluctuating somewhat with changes in cytosolic ion content. Examination of many of our micrographs of adult rabbit gastric mucosae revealed ϳ200 gastric glands per linear cm, thus ϳ40,000 glands/cm 2 . Diameter of a single gland lumen, modeled as a simple cylindrical tube, was approximated as 3 m (35,48,49), resulting in a total ϳ0.003 cm 2 of cross-sectional luminal area through which parietal cell secretion would flow to exit 1 cm 2 of flattened mucosa.…”

Upregulation of KCNQ1/KCNE1 K+channels by Klotho

“…33 KCNQ1 deficiency further impairs cell volume regulation. 28,29,[34][35][36] and affects cardiac repolarization. 37 Besides its impact on 1,25(OH) 2 D 3 formation, Klotho may regulate Na + , phosphate cotransport, 38,39 Na + /K + ATPase, 40 Ca 2+ channels, 41 and renal outer medullary K + channels 42 by more direct influence on the channels and transport proteins.…”