Kcnj16 (Kir5.1) Gene Ablation Causes Subfertility and Increases the Prevalence of Morphologically Abnormal Spermatozoa

The ability of spermatozoa to swim towards an oocyte and fertilize it depends on precise K+ permeability changes. Kir5.1 is an inwardly-rectifying potassium (Kir) channel with high sensitivity to intracellular H+ (pHi) and extracellular K+ concentration [K+]o, and hence provides a link between pHi and [K+]o changes and membrane potential. The intrinsic pHi sensitivity of Kir5.1 suggests a possible role for this channel in the pHi-dependent processes that take place during fertilization. However, despite the localization of Kir5.1 in murine spermatozoa, and its increased expression with age and sexual maturity, the role of the channel in sperm morphology, maturity, motility, and fertility is unknown. Here, we confirmed the presence of Kir5.1 in spermatozoa and showed strong expression of Kir4.1 channels in smooth muscle and epithelial cells lining the epididymal ducts. In contrast, Kir4.2 expression was not detected in testes. To examine the possible role of Kir5.1 in sperm physiology, we bred mice with a deletion of the Kcnj16 (Kir5.1) gene and observed that 20% of Kir5.1 knock-out male mice were infertile. Furthermore, 50% of knock-out mice older than 3 months were unable to breed. By contrast, 100% of wild-type (WT) mice were fertile. The genetic inactivation of Kcnj16 also resulted in smaller testes and a greater percentage of sperm with folded flagellum compared to WT littermates. Nevertheless, the abnormal sperm from mutant animals displayed increased progressive motility. Thus, ablation of the Kcnj16 gene identifies Kir5.1 channel as an important element contributing to testis development, sperm flagellar morphology, motility, and fertility. These findings are potentially relevant to the understanding of the complex pHi- and [K+]o-dependent interplay between different sperm ion channels, and provide insight into their role in fertilization and infertility.

Transepithelial glucose transport and Na+/K+ homeostasis in enterocytes: an integrative model

The uptake of glucose and the nutrient coupled transcellular sodium traffic across epithelial cells in the small intestine has been an ongoing topic in physiological research for over half a century. Driving the uptake of nutrients like glucose, enterocytes must have regulatory mechanisms that respond to the considerable changes in the inflow of sodium during absorption. The Na-K-ATPase membrane protein plays a major role in this regulation. We propose the hypothesis that the amount of active Na-K-ATPase in enterocytes is directly regulated by the concentration of intracellular Na+ and that this regulation together with a regulation of basolateral K permeability by intracellular ATP gives the enterocyte the ability to maintain ionic Na+/K+ homeostasis. To explore these regulatory mechanisms, we present a mathematical model of the sodium coupled uptake of glucose in epithelial enterocytes. Our model integrates knowledge about individual transporter proteins including apical SGLT1, basolateral Na-K-ATPase, and GLUT2, together with diffusion and membrane potentials. The intracellular concentrations of glucose, sodium, potassium, and chloride are modeled by nonlinear differential equations, and molecular flows are calculated based on experimental kinetic data from the literature, including substrate saturation, product inhibition, and modulation by membrane potential. Simulation results of the model without the addition of regulatory mechanisms fit well with published short-term observations, including cell depolarization and increased concentration of intracellular glucose and sodium during increased concentration of luminal glucose/sodium. Adding regulatory mechanisms for regulation of Na-K-ATPase and K permeability to the model show that our hypothesis predicts observed long-term ionic homeostasis.

Intracellular changes of Na+, K+, Ca++ & Mg++ in rat pancreatic islets in different glucose concentration and their relation with insulin secretion

Impairment of insulin secretion from pancreatic ?–cell constitutes an important pathophysiological factor in the development of diabetes mellitus. The changes of intracellular concentration of Na+, K+, Ca++ and Mg++ were observed in substimulatory and stimulatory different glucose concentrations. Pancreatic islets from Long-Evans rats were isolated by collagenase digestion. The concentrations of ions expressed in terms of islet protein in the homogenized islets were measured by using an ion-sensitive electrode based autoanalyzer. In the physiological medium, the islet content of all the four ions increased significantly in response to glucose with maximum level at 11 mM and no further increase at 20 mM. Initial depolarizing effect of glucose is due to reduction of K+ permeability. The reduction of K+ permeability by glucose in ?–cell is a major step in stimulus-secretion coupling for insulin release. DOI: http://dx.doi.org/10.3329/jdnmch.v18i2.16016 J. Dhaka National Med. Coll. Hos. 2012; 18 (02): 17-20

Aquaporin-4–dependent K+ and water transport modeled in brain extracellular space following neuroexcitation

Potassium (K+) ions released into brain extracellular space (ECS) during neuroexcitation are efficiently taken up by astrocytes. Deletion of astrocyte water channel aquaporin-4 (AQP4) in mice alters neuroexcitation by reducing ECS [K+] accumulation and slowing K+ reuptake. These effects could involve AQP4-dependent: (a) K+ permeability, (b) resting ECS volume, (c) ECS contraction during K+ reuptake, and (d) diffusion-limited water/K+ transport coupling. To investigate the role of these mechanisms, we compared experimental data to predictions of a model of K+ and water uptake into astrocytes after neuronal release of K+ into the ECS. The model computed the kinetics of ECS [K+] and volume, with input parameters including initial ECS volume, astrocyte K+ conductance and water permeability, and diffusion in astrocyte cytoplasm. Numerical methods were developed to compute transport and diffusion for a nonstationary astrocyte–ECS interface. The modeling showed that mechanisms b–d, together, can predict experimentally observed impairment in K+ reuptake from the ECS in AQP4 deficiency, as well as altered K+ accumulation in the ECS after neuroexcitation, provided that astrocyte water permeability is sufficiently reduced in AQP4 deficiency and that solute diffusion in astrocyte cytoplasm is sufficiently low. The modeling thus provides a potential explanation for AQP4-dependent K+/water coupling in the ECS without requiring AQP4-dependent astrocyte K+ permeability. Our model links the physical and ion/water transport properties of brain cells with the dynamics of neuroexcitation, and supports the conclusion that reduced AQP4-dependent water transport is responsible for defective neuroexcitation in AQP4 deficiency.

EFFECTS OF LOW INTENSIVE 900-MHZ RF-EMR ON ANIMAL BLOOD INDICES AFTER SINGLE ACUTE OR FRACTIONAL TOTAL BODY EXPOSURE

Functional indices of blood plasma and erythrocytes of whiterats exposed to low intensity radio-frequency electromagnetic radiation(RF-EMR) were studied. Two modes of irradiation were used: a) 1-timeaction during 2 hours, i.e. single 2-hour acute exposure; b) fractionalexposure to RF-EMR during 4 consecutive days for 0.5 hour daily.Sham-treated rats served as a Norm. On days 1, 5, 10 and 20 after thelast exposure 5 rats per observation day were sacrificed and bloodsamples were drawn to determine intensity of lipid peroxidation in bloodplasma and erythrocytes, integral antioxidant activity of water-solublenon-enzymatic antioxidants of rat blood plasma, erythrocyte membranepotential, K+ permeability across the erythrocytes membranes, and thefunctional state of the Ca2+-activated K+-channels of erythrocytes.According to data obtained, 900-MHz RF-EMR caused statisticallysignificant changes in the studied parameters both in early and lateobservation periods. Hence, the character and the dynamics of changesdepended on the mode of irradiation. Thus, a conclusion can be drawn that upon total influence on theorganism low intensive EMR with 900 MHz facilitates development oflong-lasting effect manifested as changes in functional characteristics ofblood plasma and red blood cells. Key words: 900-MHz, blood plasma, erythrocytes, membrane