ANO1 in intramuscular interstitial cells of Cajal plays a key role in the generation of slow waves and tone in the internal anal sphincter

KEY POINTS

The internal anal sphincter develops tone important for maintaining high anal pressure and continence. Controversy exists regarding the mechanisms underlying tone development. We examined the hypothesis that tone depends upon electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca²⁺ -activated Cl^- channels (ANO1, encoded by Ano1) and voltage-dependent L-type Ca²⁺ channels (Cav_L , encoded by Cacna1c). Measurement of membrane potential and contraction indicated that ANO1 and Cav_L have a central role in SW generation, phasic contractions and tone, independent of stretch. ANO1 expression was examined in wildtype and Ano1^/+egfp mice with immunohistochemical techniques. Ano1 and Cacna1c expression levels were examined by quantitative PCR in fluorescence-activated cell sorting. ICC-IM were the predominant cell type expressing ANO1 and the most likely candidate for SW generation. SWs in ICC-IM are proposed to conduct to smooth muscle where Ca²⁺ entry via Cav_L results in phasic activity that sums to produce tone.

ABSTRACT

The mechanism underlying tone generation in the internal anal sphincter (IAS) is controversial. We examined the hypothesis that tone depends upon generation of electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca²⁺ -activated Cl^- channels (encoded by Ano1) and voltage-dependent L-type Ca²⁺ channels (encoded by Cacna1c). Phasic contractions and tone in the IAS were nearly abolished by ANO1 and Cav_L antagonists. ANO1 antagonists also abolished SWs as well as transient depolarizations that persisted after addition of Cav_L antagonists. Tone development in the IAS did not require stretch of muscles, and the sensitivity of contraction to ANO1 antagonists was the same in stretched versus un-stretched muscles. ANO1 expression was examined in wildtype and Ano1^/+egfp mice with immunohistochemical techniques. Dual labelling revealed that ANO1 expression could be resolved in ICC but not smooth muscle cells (SMCs) in the IAS and rectum. Ano1, Cacna1c and Kit gene expression were the same in extracts of IAS and rectum muscles. In IAS cells isolated with fluorescence-activated cell sorting, Ano1 expression was 26.5-fold greater in ICC than in SMCs while Cacna1c expression was only 2-fold greater in SMCs than in ICC. These data support a central role for ANO1 and Cav_L in the generation of SWs and tone in the IAS. ICC-IM are the probable cellular candidate for ANO1 currents and SW generation. We propose that ANO1 and Cav_L collaborate to generate SWs in ICC-IM followed by conduction to adjacent SMCs where phasic calcium entry through Cav_L sums to produce tone.

Drug-Induced Intracranial Hypertension: The Adverse Effects of Acne Medications and Topical Retinoids

BACKGROUND

Tetracyclines and vitamin A derivatives, major components in acne care and antiaging products, have been associated with the development of drug-induced intracranial hypertension (DIIH). Treatment practices and longitudinal visual outcomes have been highly understudied in DIIH. The purpose of this study was to provide management guidelines for DIIH and report visual outcomes of patients with DIIH.

METHODS

This was a single institute ophthalmology center case-control study where patients were seen between June 1, 2012, and September 1, 2023, in the United States. Patients with an International Classification of Disease (ICD) code for IIH and meeting the IIH diagnostic criteria who were taking a tetracycline or a vitamin A derivative during their diagnosis were included in this study. Patients were stratified into the following 3 categories: tetracyclines only, vitamin A derivatives only, or both, and compared with Kruskal-Wallis rank-sum tests. Poor visual outcomes were evaluated for and defined as a visual field mean deviation (peripheral visual measure) of -7 dB or greater. Individuals were followed for up to 1.5 years after diagnosis.

RESULTS

Among patients with IIH (n = 839), DIIH occurred in 8.10% of them (n = 68) with 83% taking the medication for acne. 88% of cases were female, and patients had a mean age of 24.96 years. DIIH medications were taken for an average length of 25.79 weeks before diagnosis of IIH. 20.5% of patients with DIIH were not treated with any IIH medication and were discontinued from the inducing drug. 3 patients had a poor visual outcome on follow-up with all of them taking a vitamin A derivative (P < 0.05). Patients identified as having a poor visual outcome did not report discontinuing the DIIH drug (P < 0.05).

CONCLUSIONS

We propose treatment guidelines highlighting that patients taking a DIIH medication who develop headaches or visual changes should be immediately referred to ophthalmology, removal of the offending agent, and close monitoring by ophthalmology for vision loss. Importantly, vitamin A DIIH may have more severe visual outcomes, but further research is needed to corroborate this finding.

Idiopathic Intracranial Hypertension Is Associated With an Increased Risk of Hypertensive Pregnancy Disorders

BACKGROUND

Idiopathic intracranial hypertension (IIH) mainly occurs in women of a reproductive age who are overweight or obese. As pregnancy occurs in this age group, it is important to understand whether there are associations between IIH and pregnancy. The purpose of this study was to determine the incidence of IIH development during a pregnancy and whether IIH is associated with hypertensive disorders of pregnancy (HDP).

METHODS

In this retrospective cohort analysis, electronic health records from a tertiary care center were used to identify patients with IIH. Patients who had a diagnostic code for IIH or papilledema and were seen between June 1, 2012, and September 1, 2023, were included. After meeting the revised Dandy diagnostic criteria, patients were evaluated for a history of pregnancy before, during, or after their IIH diagnosis and hypertensive disorders including preeclampsia/eclampsia, HELLP (hemolysis, elevated liver enzymes, low platelet count) syndrome, and hypertension. Incidence and risk ratios (RR) were calculated comparing patients with IIH with controls without IIH. To corroborate these results while controlling for obesity and migraine, the TriNetX platform housing more than 100 million patients was used to design a case-control analysis evaluating the odds of an IIH patient having an HDP.

RESULTS

Two hundred ninety-two IIH patients with a prior pregnancy were identified of which 7% developed new onset IIH during pregnancy. Patients had increased risks of all HDP including eclampsia (RR: 12.92, 95% CI: 5.35, 31.22), preeclampsia (2.39, CI 1.84, 3.10), and HELLP syndrome (6.72, CI 2.16, 20.90) compared with controls. Patients with IIH also had higher risks of ectopic pregnancies and miscarriages (P < 0.05). When controlling for obesity and migraine, patients continued to have increased odds of all HDP and eclampsia (P < 0.05).

CONCLUSIONS

Patients with IIH had an increased risk of having an HDP, especially eclampsia and HELLP syndrome highlighting a need for increased clinical monitoring of these patients during pregnancy.