In the basolateral membrane of rabbit and rat gastric parietal cells, we have found a Cl^– channel (0.3-0.4 pS) which is activated via the prostaglandin E₂/Ca²⁺/nitric oxide/cyclic GMP-dependent pathway (Sakai et al. 1995). Recently, CLCA1, a Ca²⁺-activated Cl^– channel, has been suggested to be present in the basolateral membrane (Caroppo et al. 1998). In the apical membrane of rabbit parietal cells, CLC-2 channel is suggested to be associated with secretion of gastric acid (Sherry et al. 2001), although this conclusion is controversial (Jentsch et al. 1999).

Here, we investigated what kinds of Cl^– channels are expressed in rabbit gastric parietal cells. Rabbits were killed by intraperitoneal administration of an overdose of urethane (> 2 g kg^-1). Preparation of gastric parietal cells was performed as previously described (Sakai et al. 1995). The parietal cell-rich suspension contained 83-89 % of parietal cells.

The partial cDNA fragment of rabbit CLCA1 could be amplified from total RNA of tracheal epithelium. A Northern blot analysis showed that rabbit CLCA1 mRNA (3.4 kb) is highly expressed in the tracheal epithelium, although not in the gastric parietal cells. CLCA1 mRNA could not be detected even by RT-PCR in the gastric parietal cells. With RT-PCR using mRNA of rabbit gastric parietal cells and a set of degenerating primers for the CLC family, partial cDNA fragments of CLC-2, CLC-3 and CLC-5 were obtained. Northern blot analyses showed that mRNAs of CLC-2 (3.3 kb), CLC-3 (4.6 and 6.9 kb) and CLC-5 (9.5 kb) were significantly expressed in gastric parietal cells. Especially, CLC-2 mRNA was abundant. However, CLC-2 protein was not detected in the membrane fraction of parietal cells, but detected mainly in the cytosolic fraction.

These results suggest that CLCA1 may not be a Cl^– channel in the basolateral membrane, and that CLC-2 may not be a Cl^– channel in the apical membrane of rabbit parietal cells.