Inositol 1,4,5-trisphosphate mediates adrenaline activation of K+ conductance in mouse peritoneal macrophages.
In mouse peritoneal macrophages, alpha 1-adrenoceptor stimulation evokes a Ca(2+)-dependent K+ current [Io(Adr)][Hara et al. (1991) Pflügers Arch 419:371-379]. The roles of D-myo-inositol 1,4,5-trisphosphate (InsP3) and a GTP-binding protein (G protein) in Io(Adr) were investigated with tight-seal whole-cell recordings and fura-2 fluorescence measurements. Intracellular injection of InsP3 (5-50 microM) evoked transient outward currents [Io(InsP3)] with or without damped oscillations in membrane currents at -40 mV. Dialysis with 0.2 mM guanosine 5'-[3-thio]triphosphate (GTP[gamma S], a poorly hydrolysable GTP analogue) at -40 mV activated oscillatory outward currents or a slowly developing steady current on which such oscillations were superimposed after a delay of 10-90 s. Io(InsP3) and the GTP[gamma S]-induced current [Io(GTP[gamma S])] were accompanied by an increase in conductance. Reversal potentials of both responses closely depended on the extracellular K+ concentration. Fura-2 measurements revealed that Io(InsP3) and Io(GTP[gamma S]) result from a rise in intracellular free Ca2+ concentration ([Ca2+]i). Removal of extracellular Ca2+ did not abolish Io(InsP3) and Io(GTP[gamma S]). Both were blocked by bath-applied charybdotoxin. Intracellular D-myo-inositol 1,3,4,5-tetrakisphosphate (InsP4, 50 microM) did not evoke any responses, whereas D-myo-inositol 2,4,5-trisphosphate [InsP3(2,4,5), 20 microM] elicited an outward current at -40 mV. Io(InsP3) was completely blocked by prior dialysis with the InsP3 receptor antagonist heparin (5 mg/ml). Inclusion of guanosine 5'-[2-thiol] diphosphate (GDP[beta S], 2 mM) or heparin (5 mg/ml) together with GTP[gamma S] in the patch pipette solution completely blocked Io(GTP[gamma S]). These results indicate that intracellular injection of InsP3 or GTP[gamma S] mimic Io(Adr).(ABSTRACT TRUNCATED AT 250 WORDS)
Hara
N
N
Department of Physiology, Shimane Medical University, Izumo, Japan.
Ichinose
M
M
Sawada
M
M
Maeno
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology / Q000502:physiology*; D007295:Inositol Phosphates / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D010529:Peritoneal Cavity / Q000166:cytology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013873:Thionucleotides / Q000494:pharmacology
D007295:Inositol Phosphates; D015221:Potassium Channels; D011942:Receptors, Adrenergic, alpha; D013873:Thionucleotides; C081655:inositol-1,3,4,5-tetrakisphosphate; D006153:Guanosine Diphosphate; C032829:6-thioguanosine 5'-diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium