Cold acclimation increases depolarization resistance and tolerance in muscle fibers from a chill-susceptible insect, Locusta migratoria

Cold exposure depolarizes cells in insects due to a reduced electrogenic ion transport and a gradual increase in extracellular K+ concentration ([K+]). Cold-induced depolarization is linked to cold injury in chill-susceptible insects, and the locust, Locusta migratoria, has been shown to improve cold tolerance following cold acclimation through depolarization resistance. Here we investigate how cold acclimation influences depolarization resistance and how this resistance relates to improved cold tolerance. To address this question, we investigated if cold acclimation affects the electrogenic transport capacity and/or the relative K+ permeability during cold exposure by measuring membrane potentials of warm- and cold-acclimated locusts in the presence and absence of ouabain (Na+-K+ pump blocker) or 4-aminopyridine (4-AP; voltage-gated K+ channel blocker). In addition, we compared the membrane lipid composition of muscle tissue from warm- and cold-acclimated locust and the abundance of a range transcripts related to ion transport and cell injury accumulation. We found that cold-acclimated locusts are depolarization resistant due to an elevated K+ permeability, facilitated by opening of 4-AP-sensitive K+ channels. In accordance, cold acclimation was associated with an increased abundance of Shaker transcripts (gene encoding 4-AP-sensitive voltage-gated K+ channels). Furthermore, we found that cold acclimation improved muscle cell viability following exposure to cold and hyperkalemia even when muscles were depolarized substantially. Thus cold acclimation confers resistance to depolarization by altering the relative ion permeability, but cold-acclimated locusts are also more tolerant to depolarization.

A PANI supported lipid bilayer that contains NhaA transporter proteins provides a basis for a biomimetic biocapacitor

This biomimetic membrane system of Na+/H+ transport proteins in a lipid bilayer supported by polyanaline has controllable electrogenic ion transport to function as a high-speed rechargeable biocapacitor for use in bioinspired biological engineering.

Enterohemorrhagic E. coli (EHEC)—Secreted Serine Protease EspP Stimulates Electrogenic Ion Transport in Human Colonoid Monolayers

One of the characteristic manifestations of Shiga-toxin-producing Escherichia coli (E. coli) infection in humans, including EHEC and Enteroaggregative E. coli O104:H4, is watery diarrhea. However, neither Shiga toxin nor numerous components of the type-3 secretion system have been found to independently elicit fluid secretion. We used the adult stem-cell-derived human colonoid monolayers (HCM) to test whether EHEC-secreted extracellular serine protease P (EspP), a member of the serine protease family broadly expressed by diarrheagenic E. coli can act as an enterotoxin. We applied the Ussing chamber/voltage clamp technique to determine whether EspP stimulates electrogenic ion transport indicated by a change in short-circuit current (Isc). EspP stimulates Isc in HCM. The EspP-stimulated Isc does not require protease activity, is not cystic fibrosis transmembrane conductance regulator (CFTR)-mediated, but is partially Ca2+-dependent. EspP neutralization with a specific antibody reduces its potency in stimulating Isc. Serine Protease A, secreted by Enteroaggregative E. coli, also stimulates Isc in HCM, but this current is CFTR-dependent. In conclusion, EspP stimulates colonic CFTR-independent active ion transport and may be involved in the pathophysiology of EHEC diarrhea. Serine protease toxins from E. coli pathogens appear to serve as enterotoxins, potentially significantly contributing to watery diarrhea.

Proceedings from the 5th Annual University of Calgary Leaders in Medicine Research Symposium

On November 8, 2013, the Leaders in Medicine (LIM) program hosted the 5th Annual Research Symposium. Dr. Jerrold Ellner, Chief of the Infectious Diseases section at Boston Medical Centre and Professor of Medicine at Boston University School of Medicine, was the keynote speaker and presented his lecture entitled “Tuberculosis – Past, Present and Future”. The LIM symposium gives a forum for LIM as well as non-LIM medical students to present their research work as either an oral or poster presentation. There were a total of 53 abstracts presented and five oral presentations. The symposium was attended by over 100 students and more than 30 staff members. The oral presentations included • Amrita Roy, Aboriginal identity, ethnic minority status, and prenatal depressive symptoms in a longitudinal pregnancy cohort study in Alberta. • David Nicholl, Obstructive sleep apnea treatment with continuous positive airway pressure decreases intraglomerular pressure and alters renal sensitivity to angiotensin. • James Cotton, An assemblage A Giardia cathepsin B protease degrades interleukin-8 and attenuates neutrophil chemotaxis. • Krystyna Ediger, Alexander Arnold and Emily Shelton, Rebuilding the Calgary Student Run Clinic: A Model for Sustainability. • Sarah MacEachern, Inhibiting inducible nitric oxide synthase restores electrogenic ion transport in experimental IBD: a novel role for enteric glia. See the article on the University of Calgary Leaders in Medicine Program, “A Prescription that Addresses the Decline of Basic Science Education in Medical School” in this same issue of CIM for more details on the program. In short, the LIM Research Symposium has the following objectives: (1) to showcase the impressive variety of projects undertaken by students in the LIM Program as well as U of C medical students; (2) to encourage medical student participation in research and special projects; and, (3) to inform students and faculty about the diversity of opportunities available for research and special projects during medical school and beyond. The following abstracts are those that were put forward for publication.

Cyclic AMP-induced K+secretion occurs independently of Cl−secretion in rat distal colon

cAMP induces both active Cl−and active K+secretion in mammalian colon. It is generally assumed that a mechanism for K+exit is essential to maintain cells in the hyperpolarized state, thus favoring a sustained Cl−secretion. Both Kcnn4c and Kcnma1 channels are located in colon, and this study addressed the questions of whether Kcnn4c and/or Kcnma1 channels mediate cAMP-induced K+secretion and whether cAMP-induced K+secretion provides the driving force for Cl−secretion. Forskolin (FSK)-enhanced short-circuit current (indicator of net electrogenic ion transport) and K+fluxes were measured simultaneously in colonic mucosa under voltage-clamp conditions. Mucosal Na+orthovanadate (P-type ATPase inhibitor) inhibited active K+absorption normally present in rat distal colon. In the presence of mucosal Na+orthovanadate, serosal FSK induced both K+and Cl−secretion. FSK-induced K+secretion was 1) not inhibited by either mucosal or serosal 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34; a Kcnn4 channel blocker), 2) inhibited (92%) by mucosal iberiotoxin (Kcnma1 channel blocker), and 3) not affected by mucosal cystic fibrosis transmembrane conductance regulator inhibitor (CFTRinh-172). By contrast, FSK-induced Cl−secretion was 1) completely inhibited by serosal TRAM-34, 2) not inhibited by either mucosal or serosal iberiotoxin, and 3) completely inhibited by mucosal CFTRinh-172. These results indicate that cAMP-induced colonic K+secretion is mediated via Kcnma1 channels located in the apical membrane and most likely contributes to stool K+losses in secretory diarrhea. On the other hand, cAMP-induced colonic Cl−secretion requires the activity of Kcnn4b channels located in the basolateral membrane and is not dependent on the concurrent activation of apical Kcnma1 channels.