Ergonomic Evaluation on Skidding Tractors

Choroid plexus epithelial cells (CPECs) secrete cerebrospinal fluid (CSF). They express Na+-K+-ATPase and Na+-K+-2Cl− cotransporter 1 (NKCC1) on their apical membrane, deviating from typical basolateral membrane location in secretory epithelia. Given this peculiarity, the direction of basal net ion fluxes mediated by NKCC1 in CPECs is controversial, and cotransporter function is unclear. Determining the direction of basal NKCC1-mediated fluxes is critical to understanding the function of apical NKCC1. If NKCC1 works in the net efflux mode, it may be directly involved in CSF secretion. Conversely, if NKCC1 works in the net influx mode, it would have an absorptive function, contributing to intracellular Cl− concentration ([Cl−]i) and cell water volume (CWV) maintenance needed for CSF secretion. We resolve this long-standing debate by electron microscopy (EM), live-cell-imaging microscopy (LCIM), and intracellular Na+ and Cl− measurements in single CPECs of NKCC1+/+ and NKCC1−/− mouse. NKCC1-mediated ion and associated water fluxes are tightly linked, thus their direction is inferred by measuring CWV changes. Genetic or pharmacological NKCC1 inactivation produces CPEC shrinkage. EM of NKCC1−/− CPECs in situ shows they are shrunken, forming large dilations of their basolateral extracellular spaces, yet remaining attached by tight junctions. Normarski LCIM shows in vitro CPECs from NKCC1−/− are ~17% smaller than NKCC1+/+. CWV measurements in calcein-loaded CPECs show that bumetanide (10 μM) produces ~16% decrease in CWV in NKCC1+/+ but not in NKCC1−/− CPECs. Our findings suggest that under basal conditions apical NKCC1 is continuously active and works in the net inward flux mode maintaining [Cl−]i and CWV needed for CSF secretion

Intracellular Chloride Regulation

Intracellular chloride (Cl−), together with bicarbonate (HCO3−), is the most abundant free anion in living cells. Most animal cells exhibit a non-equilibrium distribution of Cl− across their plasma membranes. Some cells actively extrude Cl−, others actively accumulate it, but few cells ignore it. By virtue of being distributed out of electrochemical equilibrium, Cl− serves as a key player in a variety of cellular functions, such as intracellular pH (pHi) regulation, cell volume regulation, transepithelial salt transport, synaptic signaling (in both the depolarizing and hyperpolarizing directions), neuronal growth, migration and targeting, membrane potential stabilization, sensory transduction including nociception and extracellular K+ scavenging. Intracellular [Cl−] is determined by the interaction of various anion-transporting systems present in a cell, including Cl−channels as well as several cotransporters and exchangers. The carrier protein molecules that transport Cl−include the electroneutral Cl−/HCO3− exchangers that play a central role in pHi regulation and serve as uphill Cl−-accumulating mechanisms and the family of electroneutral cation-chloride cotransporters. This family encompasses nine members, seven of which exhibit transport activity: a Na+-Cl−cotransporter (NCC), two Na+-K+-Cl− cotransporters (NKCC1 and NKCC2) and four Na+-independent K+-Cl− cotransporters (KCC1, KCC2, KCC3 and KCC4). The cotransporter proteins share a common predicted membrane topology, with 12 putative transmembrane segments flanked by long hydrophilic amino- and carboxyl-terminal cytoplasmic domains. These carrier proteins are of high significance in the pathophysiology of several abnormalities and, because of this, they are ideal targets for translational research. Therefore, understanding their structure, function, regulation, distribution and pharmacological sensitivities is of fundamental importance

Intracellular Chloride Regulation

Intracellular chloride (Cl−), together with bicarbonate (HCO3−), is the most abundant free anion in living cells. Most animal cells exhibit a non-equilibrium distribution of Cl− across their plasma membranes. Some cells actively extrude Cl−, others actively accumulate it, but few cells ignore it. By virtue of being distributed out of electrochemical equilibrium, Cl− serves as a key player in a variety of cellular functions, such as intracellular pH (pHi) regulation, cell volume regulation, transepithelial salt transport, synaptic signaling (in both the depolarizing and hyperpolarizing directions), neuronal growth, migration and targeting, membrane potential stabilization, sensory transduction including nociception and extracellular K+ scavenging. Intracellular [Cl−] is determined by the interaction of various anion-transporting systems present in a cell, including Cl−channels as well as several cotransporters and exchangers. The carrier protein molecules that transport Cl−include the electroneutral Cl−/HCO3− exchangers that play a central role in pHi regulation and serve as uphill Cl−-accumulating mechanisms and the family of electroneutral cation-chloride cotransporters. This family encompasses nine members, seven of which exhibit transport activity: a Na+-Cl−cotransporter (NCC), two Na+-K+-Cl− cotransporters (NKCC1 and NKCC2) and four Na+-independent K+-Cl− cotransporters (KCC1, KCC2, KCC3 and KCC4). The cotransporter proteins share a common predicted membrane topology, with 12 putative transmembrane segments flanked by long hydrophilic amino- and carboxyl-terminal cytoplasmic domains. These carrier proteins are of high significance in the pathophysiology of several abnormalities and, because of this, they are ideal targets for translational research. Therefore, understanding their structure, function, regulation, distribution and pharmacological sensitivities is of fundamental importance

Physiology and Pathology of Chloride Transporters and Channels in the Nervous System: From Molecules to Diseases

The importance of chloride ions in cell physiology has not been fully recognized until recently, in spite of the fact that chloride (Cl-), together with bicarbonate, is the most abundant free anion in animal cells, and performs or determines fundamental biological functions in all tissues. For many years it was thought that Cl- was distributed in thermodynamic equilibrium across the plasma membrane of most cells. Research carried out during the last couple of decades has led to a dramatic change in this simplistic view. We now know that most animal cells, neurons included, exhibit a non-equilibrium distribution of Cl- across their plasma membranes. Over the last 10 to 15 years, with the growth of molecular biology and the advent of new optical methods, an enormous amount of exciting new information has become available on the molecular structure and function of Cl- channels and carriers. In nerve cells, Cl- channels and carriers play key functional roles in GABA- and glycine-mediated synaptic inhibition, neuronal growth and development, extracellular potassium scavenging, sensory-transduction, neurotransmitter uptake and cell volume control. Disruption of Cl- homeostasis in neurons underlies pathological conditions such as epilepsy, deafness, imbalance, brain edema and ischemia, pain and neurogenic inflammation. This book is about how chloride ions are regulated and how they cross the plasma membrane of neurons. It spans from molecular structure and function of carriers and channels involved in Cl- transport to their role in various diseases