0000000000395781
AUTHOR
Jana F. Liewald
Proton conductance of human transient receptor potential-vanilloid type-1 expressed in oocytes of Xenopus laevis and in Chinese hamster ovary cells.
Transient receptor potential-vanilloid type-1 (TRPV1) is a ligand-gated cation channel with preference for divalent cations, especially Ca(2+) (sequence of conductances: Ca(2+)Mg(2+)Na(+) approximately/= K(+) approximately/= Cs(+)). In the present study, the two-electrode voltage-clamp technique was used on oocytes of Xenopus laevis expressing TRPV1 to evaluate whether human TRPV1 also conducts protons. In medium devoid of K(+), Na(+), Mg(2+), and Ca(2+), capsaicin 1 microM induced a significant inward current (62% of the current in physiological medium). The effects of capsaicin were abolished in the presence of capsazepine 3 microM. The capsaicin-induced currents in medium devoid of Na(+)…
Signal transduction in isolated fat body from the cockroach Blaptica dubia exposed to hypertrehalosaemic neuropeptide
Hypertrehalosaemic hormones stimulate trehalogenesis while inhibiting glycolysis in cockroach fat body. Signal transduction of the hypertrehalosaemic peptide Bld HrTH was examined in isolated fat body of the Argentine cockroach Blaptica dubia with respect to its effects on the increase in trehalose production and decrease in the content of the glycolytic activator fructose 2,6-bisphosphate in the tissue. Cyclic AMP does not seem to be involved in these processes as the cAMP analogue cpt-cAMP and the phosphodiesterase inhibitor IBMX, which both permeate cell membranes, had no effect on either parameter. Octopamine at physiological concentrations (10−7 mol · l−1) was also ineffective, but at …
Antagonistic effects of hypertrehalosemic neuropeptide on the activities of 6-phosphofructo-1-kinase and fructose-1,6-bisphosphatase in cockroach fat body
Hypertrehalosemic neuropeptides from the corpora cardiaca such as the decapeptide Bld HrTH bring about a profound switch in the metabolic activity of cockroach fat body during which production of the blood sugar trehalose is stimulated while the catabolism of carbohydrate (glycolysis) is inhibited. The mechanisms of the metabolic switch are not fully understood. Incubation of isolated fat body from the cockroach Blaptica dubia with 10(-8) M Bld HrTH, for 10-60 min, stimulated glycogen breakdown and increased the content of the substrates of both the glycolytic enzyme 6-phosphofructo-1-kinase (PFK, EC 2.7.1.11) and the gluconeogenic enzyme fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11) in…
Monovalent cation conductance in Xenopus laevis oocytes expressing hCAT-3
hCAT-3 (human cationic amino acid transporter type three) was investigated with both the two-electrode voltage clamp method and tracer experiments. Oocytes expressing hCAT-3 displayed less negative membrane potentials and larger voltage-dependent currents than native or water-injected oocytes did. Ion substitution experiments in hCAT-3-expressing oocytes revealed a large conductance for Na + and K + . In the presence of l-Arg, voltage-dependent inward and outward currents were observed. At symmetrical (inside/outside) concentrations of l-Arg, the conductance of the transporter increased monoexponentially with the l-Arg concentrations; the calculated Vmax and KM values amounted to 8.3 AS and…
Intracellular accumulation of l-Arg, kinetics of transport, and potassium leak conductance in oocytes from Xenopus laevis expressing hCAT-1, hCAT-2A, and hCAT-2B
AbstractCationic amino acid transporters play an important role in the intracellular supply of l-Arg and the generation of nitric oxide. Since the transport of l-Arg is voltage-dependent, we aimed at determining the intracellular l-Arg concentration and describing the transport of l-Arg in terms of Michaelis–Menten kinetics, taking into account membrane voltage. The human isoforms of the cationic amino acid transporters, hCAT-1, hCAT-2A, and hCAT-2B, were expressed in oocytes from Xenopus laevis and studied with the voltage clamp technique and in tracer experiments. We found that l-Arg was concentrated intracellularly by all hCAT isoforms and that influx and efflux, in the steady state of e…