Hepatic metabolism and gene expression are among other regulatory mechanisms controlled by the cellular hydration state, which changes rapidly in response to anisotonicity, concentrative substrate uptake, oxidative stress, and under the inf luence of hormones such as insulin and glucagon. Differential screening for cell volume sensitive transcripts in a human hepatoma cell line revealed a gene for a putative serine͞threonine kinase, h-sgk, which has 98% sequence identity to a serum-and glucocorticoid regulated kinase, sgk, cloned from a rat mammary tumor cell line. h-sgk transcript levels were strongly altered during anisotonic and isotonic cell volume changes. Within 30 min h-sgk RNA was, independent of de novo protein synthesis, induced upon cell shrinkage and, due to a complete stop in h-sgk transcription, reduced upon cell swelling. Comparable changes of sgk transcript levels were observed in a renal epithelial cell line. h-sgk mRNA was detected in all human tissues tested, with the highest levels in pancreas, liver, and heart. The putative serine͞threonine protein kinase h-sgk may provide a functional link between the cellular hydration state and metabolic control.
The effect of arginine vasopressin (AVP) on transepithelial Ca2+ transport in primary cultures of rabbit cortical collecting system cells was examined. Addition of AVP to the basolateral side of the monolayer dose-dependently (ECM ) = 0.7 nM) increased active Ca2+ reab sorption from a basal value of 85 ± 2 nm oM r'-cnr2 to a maximum value of 124 ± 3 nniol-lr^cnr2. This was par alleled by a dose-dependent (ECi0 =1.1 nM ) increase in cellular adenosine ¿'^'-cyclic monophosphate (cAMP) content. Both effects of AVP were mimicked by the V 2 agonist deamino-Cys,D-Arg8-vasopressin (dDAVP) and forskolin. Addition of either AVP or dDAVP to the baso lateral side evoked a sustained increase in cytosolic free Ca2+ concentration, which resulted from both Ca2* entry and release from internal stores. Only the effect on Ca2+ entry was mimicked by forskolin, demonstrating that cAMP acts by activating a Ca2* influx pathway. The pres ent findings demonstrate that AVP stimulates transeellular Ca2'1 * transport in the cortical collecting system through activation of basolateral V 2 receptors coupled to adenylyl cyclase to increase the cellular cAM P content.
1. The effects of isosorbiddinitrate (ISDN) were tested on membrane currents and resting potential in Xenopus laevis oocytes which were either uninjected or injected with cRNA encoding for K+ channels from three distinct families (slowly activating IK channels, delayed-rectifying Kvl.1 or inwardly rectifying IRK1 K+ channels).2. In uninjected oocytes ISDN (1 mM) resulted in a decrease of the holding current at potentials more positive than -100 mV and in an increase at potentials below -100 mV.Increasing extracellular K+ to 100 mm shifted the reversal potential for ISDN-mediated effects to approximately -12 mV, suggesting an inhibition of a K+ conductance by ISDN. 3. In current clamp studies ISDN (1 mM) and Ba2+ (3 mM) depolarized cell membrane. ISDN and Ba2+ had no additive effects on membrane potential when applied simultaneously. In voltage clamp studies, corresponding results were observed for the effects of ISDN and Ba2+ on the holding current with an apparent Km of 0-21 and 0-08 mm, respectively. 4. In contrast to ISDN, the nitric oxide (NO) donors isosorbidmononitrate (ISMN) and S-nitrosocysteine (SNOC) had no effects on the holding currents in Xenopus oocytes. Moreover, the guanylate inhibitor LY 83583 did not affect ISDN-mediated holding current alterations, suggesting that ISDN acts independently of the second messenger NO. 5. ISDN inhibited exogenously expressed I8K channels with an apparent Km of 0415 mm, but at 1 mm only weakly inhibited Kvl.1 and IRKI channels. 6. It is concluded that ISDN inhibits an endogenous K+ conductance in Xenopus oocytes with a similar potency to that shown by expressed ISK channels. These effects are independent of the second messenger NO.
Slowly activating IsK channels were expressed in Xenopus oocytes and exposed to oxidative agents. Oxidative treatment reduced the resulting current IsK, while no inhibition was observed for IsK protein mutants carrying a Ser mutation instead of a highly conserved Cys residue in the intracellular domain. In contrast, Hg2+, which may not only oxidize thiol groups but also form chelates with dibasic amino acids, caused a use-dependent, positive regulation of IsK. This effect was reversed in an IsK protein mutant with a deletion in the extracellular domain. These data suggest opposite effects of peroxides and Hg2+ on IsK, a peroxide-mediated IsK inhibition by intracellular oxidation and a Hg(2+)-mediated IsK increase, caused by extracellular Hg2+ chelation of the IsK protein.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.