Role of Ca(2+)-activated K(+) channels in acetylcholine-induced dilatation of the basilar artery in vivo

1. We tested the hypothesis that activation of large conductance calcium-activated potassium channels is involved in dilator responses of the basilar artery to acetylcholine in vivo. Using a cranial window in anaesthetized rats, we examined responses of the basilar artery to acetylcholine. 2. Topical application of acetylcholine (10(−6) and 10(−5) M) increased diameter of the basilar artery from 238±7 μm to 268±7 and 288±7 μm, respectively (P<0.05 vs. baseline diameter). Iberiotoxin (10(−8) M), an inhibitor of large conductance calcium-activated potassium channels, did not affect baseline diameter of the basilar artery. In the presence of 10(−8) M iberiotoxin, 10(−6) and 10(−5) M acetylcholine increased diameter of the basilar artery from 239±7 μm to 246±7 and 261±7 μm, respectively. Thus, iberiotoxin attenuated acetylcholine-induced dilatation of the basilar artery (P<0.05). 3. Sodium nitroprusside (10(−7) and 10(−6) M) increased diameter of the basilar artery from 242±9 μm to 310±12 and 374±13 μm, respectively (P<0.05 vs. baseline diameter). In the presence of iberiotoxin (10(−8) M), sodium nitroprusside (10(−7) and 10(−6) M) increased diameter of the basilar artery from 243±6 μm to 259±9 and 311±12 μm, respectively. Thus, iberiotoxin attenuated dilator responses of the basilar artery to sodium nitroprusside (P<0.05). 4. Iberiotoxin partly inhibited dilator responses of the basilar artery to forskolin, a direct activator of adenylate cyclase, but did not affect vasodilatation produced by levcromakalim, a potassium channel opener. 5. These results suggest that dilator responses of the basilar artery to acetylcholine and sodium nitroprusside are mediated, in part, by activation of large conductance calcium-activated potassium channels. Because both acetylcholine and sodium nitroprusside have been shown to activate guanylate cyclase via nitric oxide, activation of large conductance calcium-activated potassium channels may be one of the major mechanisms by which cyclic GMP causes dilatation of the basilar artery in vivo

A Hereditary Enteropathy Caused by Mutations in the <i>SLCO2A1</i> Gene, Encoding a Prostaglandin Transporter

<div><p>Previously, we proposed a rare autosomal recessive inherited enteropathy characterized by persistent blood and protein loss from the small intestine as chronic nonspecific multiple ulcers of the small intestine (CNSU). By whole-exome sequencing in five Japanese patients with CNSU and one unaffected individual, we found four candidate mutations in the <i>SLCO2A1</i> gene, encoding a prostaglandin transporter. The pathogenicity of the mutations was supported by segregation analysis and genotyping data in controls. By Sanger sequencing of the coding regions, 11 of 12 other CNSU patients and 2 of 603 patients with a diagnosis of Crohn’s disease were found to have homozygous or compound heterozygous <i>SLCO2A1</i> mutations. In total, we identified recessive <i>SLCO2A1</i> mutations located at seven sites. Using RT-PCR, we demonstrated that the identified splice-site mutations altered the RNA splicing, and introduced a premature stop codon. Tracer prostaglandin E2 uptake analysis showed that the mutant SLCO2A1 protein for each mutation exhibited impaired prostaglandin transport. Immunohistochemistry and immunofluorescence analyses revealed that SLCO2A1 protein was expressed on the cellular membrane of vascular endothelial cells in the small intestinal mucosa in control subjects, but was not detected in affected individuals. These findings indicate that loss-of-function mutations in the <i>SLCO2A1</i> gene encoding a prostaglandin transporter cause the hereditary enteropathy CNSU. We suggest a more appropriate nomenclature of “chronic enteropathy associated with <i>SLCO2A1</i> gene” (CEAS).</p></div

Pedigrees of the families with chronic nonspecific multiple ulcers of the small intestine.

<p>The segregation of the <i>SLCO2A1</i> mutations c.1461+1G>C (splice site, family A), c.940+1G>A (splice site, families B and C), c.664G>A (G222R, family D), and c.1807C>T (R603X, family D) is indicated. Squares represent male family members, circles represent female family members, black symbols represent clinically affected family members, and slashes represent deceased family members. Arrows indicate individuals whose DNA was analyzed by whole-exome sequencing. WT denotes wild-type.</p

Clinical images of an individual with chronic nonspecific multiple ulcers of the small intestine (patient A-V–2).

<p>(A, B) Retrograde ileoscopy shows active circular and oblique multiple ulcers with mucous exudates in the ileum. (C, D) A barium follow-through examination with compression shows multiple circular barium flecks (C), eccentric deformities, and strictures (D) in the ileum. (E, F) Radiographs of the hands and tibiofibulae show no obvious abnormalities such as cortical thickening of the metacarpals and periosteal hyperostosis.</p