Proceedings of the National Academy of Sciences of the United States of America
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Proc. Natl. Acad. Sci. U.S.A. · Nov 1995
Blocking effects of polyunsaturated fatty acids on Na+ channels of neonatal rat ventricular myocytes.
Recent evidence indicates that polyunsaturated long-chain fatty acids (PUFAs) prevent lethal ischemia-induced cardiac arrhythmias in animals and probably in humans. To increase understanding of the mechanism(s) of this phenomenon, the effects of PUFAs on Na+ currents were assessed by the whole-cell patch-clamp technique in cultured neonatal rat ventricular myocytes. Extracellular application of the free 5,8,11,14,17-eicosapentaenoic acid (EPA) produced a concentration-dependent suppression of ventricular, voltage-activated Na+ currents (INa). ⋯ Also, the EPA-induced inhibition of INa was voltage dependent, since 10 microM EPA produced 83% +/- 7% and 29% +/- 5% inhibition of INa elicited by pulses from -80 to -30 mV and from -150 to -30 mV, respectively, in single-step voltage changes. A concentration of 10 microM EPA shifted the steady-state inactivation curve of INa by -19 +/- 3 mV (n = 7; P < 0.01). These effects of PUFAs on INa may be important for their antiarrhythmic effect in vivo.
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Proc. Natl. Acad. Sci. U.S.A. · Nov 1995
Ultra-low concentrations of naloxone selectively antagonize excitatory effects of morphine on sensory neurons, thereby increasing its antinociceptive potency and attenuating tolerance/dependence during chronic cotreatment.
Ultra-low picomolar concentrations of the opioid antagonists naloxone (NLX) and naltrexone (NTX) have remarkably potent antagonist actions on excitatory opioid receptor functions in mouse dorsal root ganglion (DRG) neurons, whereas higher nanomolar concentrations antagonize excitatory and inhibitory opioid functions. Pretreatment of naive nociceptive types of DRG neurons with picomolar concentrations of either antagonist blocks excitatory prolongation of the Ca(2+)-dependent component of the action potential duration (APD) elicited by picomolar-nanomolar morphine and unmasks inhibitory APD shortening. ⋯ These in vitro studies suggested that ultra-low doses of NLX or NTX that selectively block the excitatory effects of morphine may not only enhance the analgesic potency of morphine and other bimodally acting opioid agonists but also markedly attenuate their dependence liability. Subsequent correlative studies have now demonstrated that cotreatment of mice with morphine plus ultra-low-dose NTX does, in fact, enhance the antinociceptive potency of morphine in tail-flick assays and attenuate development of withdrawal symptoms in chronic, as well as acute, physical dependence assays.
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Proc. Natl. Acad. Sci. U.S.A. · Jul 1995
Evidence that neuronal G-protein-gated inwardly rectifying K+ channels are activated by G beta gamma subunits and function as heteromultimers.
Guanine nucleotide-binding proteins (G proteins) activate K+ conductances in cardiac atrial cells to slow heart rate and in neurons to decrease excitability. cDNAs encoding three isoforms of a G-protein-coupled, inwardly rectifying K+ channel (GIRK) have recently been cloned from cardiac (GIRK1/Kir 3.1) and brain cDNA libraries (GIRK2/Kir 3.2 and GIRK3/Kir 3.3). Here we report that GIRK2 but not GIRK3 can be activated by G protein subunits G beta 1 and G gamma 2 in Xenopus oocytes. ⋯ On the other hand, coexpression of GIRK3 with GIRK2 suppressed the GIRK2 alone response. These studies suggest that formation of heteromultimers involving the several GIRKs is an important mechanism for generating diversity in expression level and function of neurotransmitter-coupled, inward rectifier K+ channels.
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Proc. Natl. Acad. Sci. U.S.A. · Jun 1995
Comparative StudyThe Ste locus, a component of the parasitic cry-Ste system of Drosophila melanogaster, encodes a protein that forms crystals in primary spermatocytes and mimics properties of the beta subunit of casein kinase 2.
Males of Drosophila melanogaster lacking the Y chromosome-linked crystal locus show multiple meiotic alterations including chromosome disorganization and prominent crystal formation in primary spermatocytes. These alterations are due to the derepression of the X chromosome-linked Stellate sequences. ⋯ Immunostaining of crystal- testes has clearly shown that the Stellate protein is a major component of the crystals. Moreover, in vitro experiments have shown that this protein can interact with the catalytic alpha subunit of casein kinase 2 enzyme, altering its activity.
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Proc. Natl. Acad. Sci. U.S.A. · May 1995
Overexpressed Ly-6A.2 mediates cell-cell adhesion by binding a ligand expressed on lymphoid cells.
The Ly-6 locus encodes several cell surface proteins whose functions are unknown. Although it is hypothesized that these proteins may be receptors, there is no direct evidence that they bind a ligand. Herein we present evidence that Ly-6A.2, a Ly-6 protein expressed on T lymphocytes, binds a ligand expressed on normal thymocytes and splenic B and T cells. ⋯ Paraformaldehyde-fixed Tg+ thymocytes reaggregate in culture and this aggregation is also blocked by phosphatidyl-inositol-specific phospholipase C and anti-Ly-6A.2 monoclonal antibodies. These results indicate that the homotypic adhesion of cultured Ly-6A.2 transgenic thymocytes is directly mediated by Ly-6A.2 and, more importantly, strongly suggests that Ly-6A.2 binds a ligand that is expressed on thymocytes. Tg+ thymocytes also bind to nontransgenic thymocytes, B cells, and T cells, indicating that normal cells naturally express the Ly-6A.2 ligand.