Key role for Kv11.1 (ether-a-go-go related gene) channels in rat bladder contractility

Overview of Lymphatic Muscle Cells in Development, Physiology, and Disease

Lymphatic muscle cells (LMCs) are indispensable for proper functioning of the lymphatic system, as they provide the driving force for lymph transport. Recent studies have advanced our understanding of the molecular mechanisms that regulate LMCs, which control rhythmic contraction and vessel tone of lymphatic vessels-traits also found in cardiac and vascular smooth muscle. In this review, we discuss the molecular pathways that orchestrate LMC-mediated contractility and summarize current knowledge about their developmental origin, which may shed light on the distinct contractile characteristics of LMCs. Further, we highlight the growing evidence implicating LMC dysregulation in the pathogenesis of lymphedema and other diseases related to lymphatic vessel dysfunction. Given the limited number and efficacy of existing therapies to treat lymphedema, LMCs present a promising focus for identifying novel therapeutic targets aimed at improving lymphatic vessel contractility. Here, we discuss LMCs in health and disease, as well as therapeutic strategies aimed at targeting them to improve lymphatic vessel function.

Cycling matters: Sex hormone regulation of vascular potassium channels

Sex hormones and the reproductive cycle (estrus in rodents and menstrual in humans) have a known impact on arterial function. In spite of this, sex hormones and the estrus/menstrual cycle are often neglected experimental factors in vascular basic preclinical scientific research. Recent research by our own laboratory indicates that cyclical changes in serum concentrations of sex -hormones across the rat estrus cycle, primary estradiol, have significant consequences for the subcellular trafficking and function of KV. Vascular potassium channels, including KV, are essential components of vascular reactivity. Our study represents a small part of a growing field of literature aimed at determining the role of sex hormones in regulating arterial ion channel function. This review covers key findings describing the current understanding of sex hormone regulation of vascular potassium channels, with a focus on KV channels. Further, we highlight areas of research where the estrus cycle should be considered in future studies to determine the consequences of physiological oscillations in concentrations of sex hormones on vascular potassium channel function.

ERG K+ channels mediate a major component of action potential repolarization in lymphatic muscle

Smooth muscle cells in the walls of collecting lymphatic vessels fire spontaneous action potentials (APs), which conduct rapidly over the muscle layer to initiate contractions that propel lymph. Several ion channels have been implicated in the currents underlying the AP spike and the preceding diastolic depolarization, but the molecular identities of K+ channels involved in AP repolarization are unknown. Based on previous studies of other rhythmically active smooth muscles, we hypothesized that ether-a-go-go related gene (ERG) K+ channels (Kv11) play an important role in repolarization of the AP in lymphatic muscle. Message for one or more ERG channel isoforms was detected by RT-PCR analysis of lymphatic vessels from mice, rats and humans. Membrane potential recordings in smooth muscle cells of rat and human lymphatics revealed that nanomolar concentrations of ERG-1 inhibitors (E-4031 and BeKm-1) prolonged the duration of the AP plateau (normally ~ 1 s in duration) and induced multiple spikes, whereas ERG-1 activators (ICA-105574 and RPR-260243) shortened the plateau and could completely inhibit spontaneous APs. At relatively high inhibitor concentrations, the AP plateau duration lasted as long as 24 s. ERG activators reversed the effects of ERG inhibitors and vice-versa. In pressure myograph studies, ERG channel inhibition prolonged the diastolic repolarization phase of the contraction cycle and reduced the frequency of spontaneous contractions. This is the first evidence for a specific K+ channel contributing to the AP in lymphatic muscle. Our results imply that lymphatic contractile dysfunction may occur in long QT type II patients with mutations that result in ERG channel loss-of-function or impaired trafficking of the channel to the cell membrane.