Tetraethylammonium ion sensitivity of a 35-pS CA2(+)-activated K+ channel in GH3 cells that is activated by thyrotropin-releasing hormone.
Single Ca2(+)-activated K+ channels were studied in membrane patches from the GH3 anterior pituitary cell line. We have previously demonstrated the coexistence of large-conductance and small-conductance (280 pS and 11 pS in symmetrical 150 mM K+, respectively) Ca2(+)-activated K+ channels in this cell line (Lang and Ritchie 1987). Here we report the existence of a third type of Ca2(+)-activated K+ channel that has a conductance of about 35 pS under similar conditions. In excised inside-out patches, this channel can be activated by elevations of the internal free Ca2+ concentration, and the open probability increases as the membrane potential is made more positive. In excised patches, the sensitivity of this 35-pS channel to internal Ca2+ is low; at positive membrane potentials, this channel requires Ca2+ concentrations greater than 10 microM for activation. However, 35-pS channels have a much higher sensitivity to Ca2+ in the first minute after excision (activated by 1 microM Ca2+ at -50 mV). Therefore, it is possible that the Ca2+ sensitivity of this channel is stabilized by intracellular factors. In cell-attached patches, this intermediate conductance channel can be activated (at negative membrane potentials) by thyrotropin-releasing hormone-induced elevations of the intracellular Ca2+ concentration and by Ca2+ influx during action potentials. The intermediate conductance channel is inhibited by high concentrations of external tetraethylammonium ions (Kd = 17 mM) and is relatively resistant to inhibition by apamin.
Lang
D G
DG
Department of Physiology and Biophysics, University of Texas Medical Branch Galveston 77550.
Ritchie
A K
AK
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D001030:Apamin; D013973:Thyrotropin-Releasing Hormone; D019789:Tetraethylammonium; D002118:Calcium