Lee SK, Boron WF, Parker MD. Relief of autoinhibition of the electrogenic Na-HCO 3 cotransporter NBCe1-B: role of IRBIT vs. aminoterminal truncation.

Hill J, Lee SK, Samasilp P, Smith C. Pituitary adenylate cyclaseactivating peptide enhances electrical coupling in the mouse adrenal medulla. Am J Physiol Cell Physiol 303: C257-C266, 2012. First published May 16, 2012; doi:10.1152/ajpcell.00119.2012.-Neuroendocrine adrenal medullary chromaffin cells receive synaptic excitation through the sympathetic splanchnic nerve to elicit catecholamine release into the circulation. Under basal sympathetic tone, splanchnicreleased acetylcholine evokes chromaffin cells to fire action potentials, leading to synchronous phasic catecholamine release. Under elevated splanchnic firing, experienced under the sympathoadrenal stress response, chromaffin cells undergo desensitization to cholinergic excitation. Yet, stress evokes a persistent and elevated adrenal catecholamine release. This sustained stress-evoked release has been shown to depend on splanchnic release of a peptide transmitter, pituitary adenylate cyclase-activating peptide (PACAP). PACAP stimulates catecholamine release through a PKC-dependent pathway that is mechanistically independent of cholinergic excitation. Moreover, it has also been reported that shorter term phospho-regulation of existing gap junction channels acts to increase junctional conductance. In this study, we test if PACAP-mediated excitation upregulates cell-cell electrical coupling to enhance chromaffin cell excitability. We utilize electrophysiological recordings conducted in adrenal tissue slices to measure the effects of PACAP stimulation on cell coupling. We report that PACAP excitation increases electrical coupling and the spread of electrical excitation between adrenal chromaffin cells. Thus PACAP acts not only as a secretagogue but also evokes an electrical remodeling of the medulla, presumably to adapt to the organism's needs during acute sympathetic stress. acute stress; catecholamine; connexin-43; connexin-36; gap junction ADRENAL MEDULLARY CHROMAFFIN cells are neural crest-derived neurosecretory cells that release catecholamine into the bloodstream (2). Chromaffin cells are innervated by the bifurcating sympathetic splanchnic nerve. Under sympathetic tone, corresponding to the "rest and digest" metabolic state, the splanchnic nerve fires at a modest rate to maintain catecholamine homeostasis. Splanchnic-released acetylcholine binds to nicotinic ionotropic receptors on the chromaffin cell membrane, leading to action potential firing and controlled, phasic catecholamine release (1,7,13,18). Under the acute sympathetic stress response, the splanchnic nerve fires at a heightened rate, leading to rapid and robust cholinergic-evoked catecholamine secretion (25). Yet, the cholinergic pathway rapidly desensitizes (4, 5, 29) while elevated catecholamine secretion persists (44). Pituitary adenylate cyclase-activating peptide (PACAP) is a noncholinergic splanchnic-derived peptide transmitter released selectively during elevated splanchnic firing. PACAP has been identified as the peptide transmitter driving tonic catecholamine secretion after desensi...

Determining the effective concentration (i.e., activity) of ions in and around living cells is important to our understanding of the contribution of those ions to cellular function. Moreover, monitoring changes in ion activities in and around cells is informative about the actions of the transporters and/or channels operating in the cell membrane. The activity of an ion can be measured using a glass microelectrode that includes in its tip a liquid-membrane doped with an ion-selective ionophore. Because these electrodes can be fabricated with tip diameters that are less than 1 μm, they can be used to impale single cells in order to monitor the activities of intracellular ions. This review summarizes the history, theory, and practice of ion-selective microelectrode use and brings together a number of classic and recent examples of their usefulness in the realm of physiological study.

The death effector domain (DED) of the mammalian apoptosis mediator, Fas-associated death domain protein (FADD), induces Escherichia coli cell death under aerobic culture conditions, yet the mechanisms by which FADD-DED induces cell death are not fully understood. Oxidative stress has been implicated as one of the mechanisms. Using a proteomic approach and validation by coexpression analysis, we illustrate that overexpression of FADD-DED in E. coli invokes protein expression changes that facilitate conversion of pro-oxidant NADH into antioxidant NADPH. Typically, isocitrate dehydrogenase, phosphoenolpyruvate carboxykinase, and pyruvate kinase are downregulated and malate dehydrogenase is upregulated. We reasoned that such a change in E. coli cells is an active response to reduce the size of the NADH pool, thereby decreasing the level of ROS generation. From the coexpression studies, we observed that DNA binding protein Hns, which induces growth arrest when overexpressed heterologously, alleviated the cell killing effect of FADD-DED. FADD-DED was expressed as a noncovalently linked multimeric protein in the membrane of E. coli. Exogenous treatment of E. coli cells with FADD-DED in the presence of a membrane component induced cell death, which was accompanied by a shift of the redox balance and a decrease in the cellular ATP level. Cell death was blocked by prior expression of thioredoxin. Localization of FADD-DED to the membrane may shift the cells into a state that stimulates and fuels ROS generation. The cell death mechanism mediated by ROS may mimic antibiotic-mediated bacterial cell death or Bax-mediated apoptosis in mammalian cells. Our results provide a common mechanistic feature of ROS-involved cell death throughout prokaryotes and eukaryotes.

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