Gap junctional channels regulate acid secretion in the mammalian gastric gland.

Gap junction channels are regarded as a primary pathway for intercellular message transfer, including calcium wave propagation. Our study identified two gap junctional proteins, connexin26 and connexin32, in rat gastric glands by RT-PCR, Western blot analysis, and immunofluorescence. We demonstrated a potential physiological role of the gap junctional channels in the acid secretory process using the calcium indicator fluo-3, and microinjection of Lucifer Yellow. Application of gastrin (10-7 m) to the basolateral membrane resulted in the induction of uniphasic calcium signals in adjacent parietal cells. In addition, single parietal cell microinjections in intact glands with the cell-impermeant dye Lucifer Yellow resulted in a transfer of dye from the injected cell to the adjacent parietal cell following gastrin stimulation, demonstrating gastrin-induced cell-to-cell communication. Both calcium wave propagation and Lucifer Yellow transfer were blocked by the gap junction inhibitor 18alpha-glycyrrhetinic acid. Our studies demonstrate that functional gap junction channels in gastric glands provide an effective means for rapid cell-to-cell communication and allow for the rapid onset of acid secretion.

The stomach divalent ion-sensing receptor scar is a modulator of gastric acid secretion.

Divalent cation receptors have recently been identified in a wide variety of tissues and organs, yet their exact function remains controversial. We have previously identified a member of this receptor family in the stomach and have demonstrated that it is localized to the parietal cell, the acid secretory cell of the gastric gland. The activation of acid secretion has been classically defined as being regulated by two pathways: a neuronal pathway (mediated by acetylcholine) and an endocrine pathway (mediated by gastrin and histamine). Here, we identified a novel pathway modulating gastric acid secretion through the stomach calcium-sensing receptor (SCAR) located on the basolateral membrane of gastric parietal cells. Activation of SCAR in the intact rat gastric gland by divalent cations (Ca(2+) or Mg(2+)) or by the potent stimulator gadolinium (Gd(3+)) led to an increase in the rate of acid secretion through the apical H+,K+ -ATPase. Gd(3+) was able to activate acid secretion through the omeprazole-sensitive H+,K+ -ATPase even in the absence of the classical stimulator histamine. In contrast, inhibition of SCAR by reduction of extracellular cations abolished the stimulatory effect of histamine on gastric acid secretion, providing evidence for the regulation of the proton secretory transport protein by the receptor. These studies present the first example of a member of the divalent cation receptors modulating a plasma membrane transport protein and may lead to new insights into the regulation of gastric acid secretion.

Structure of the gene for the human 17beta-hydroxysteroid dehydrogenase type IV.

The 17beta-hydroxysteroid dehydrogenase type IV (17beta-HSD IV) is a multifunctional enzyme that is localized in the peroxisomes. The N-terminal part has dehydrogenase activity, the central part has hydratase activity, and the carboxy-terminal part is responsible for sterol transport. Recent observations of mutations in the human 17beta-HSD IV cDNA leading to a severe peroxisomal disorder motivated us to define the genomic organization of this gene mapped to Chromosome (Chr) 5q2. We show here that this gene consist of 24 exons and 23 introns with classical intron-exon junctions spanning more than 100 kbp. By mapping the regulatory region of this gene, we have shown that the first 400 bp upstream of the transcription start site are sufficient to activate transcription. The data presented here will permit sequence analysis of patients with peroxisomal disorders.