Characterization of hyperpolarization-activated cation currents in mouse anterior pituitary, AtT20 D16:16 corticotropes.
The properties of the hyperpolarization-activated inward cation current (Ih) in mouse anterior pituitary, AtT20 D16:16 corticotropes was characterized by whole cell patch clamp recording. In response to hyperpolarizing steps a large, slowly activating, voltage-dependent inward current was activated with a half maximal activation voltage (V0.5) of -96.2+/-3.1 mV with a time constant of 168+/-13 msec determined at -140 mV at room temperature. Ih had a reversal potential of -35.5+/-1.0 mV and -23.3+/-1.4 mV using 5 mM and 25 mM extracellular K+, respectively, with a relative permeability ratio for Na+ and K+ of 0.24. The current was completely blocked by 2 mM extracellular CsCl and partially blocked by ZD7288 (100 microM) but was unaffected by TEA (10 mM) or Ba2+ (1 mM). RT-PCR analysis revealed robust expression of HCN1, but not HCN2 or HCN3, subunits of hyperpolarization-activated cation channels. The endogenous Ih current was weakly activated by cAMP but robustly inhibited by the cAMP antagonist, Rp-8-CPT-cAMPS. Activation or suppression of protein kinase C activity had no significant effect on the Ih current. The data suggest that in AtT20 D16:16 corticotropes Ih is tonically regulated by the cAMP-signaling cascade and may serve to limit excessive hyperpolarization.
Department of Biomedical Sciences, University of Edinburgh Medical School, Scotland, United Kingdom.
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D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology; D054815:Cyclic Nucleotide-Gated Cation Channels; D004553:Electric Conductivity; D004789:Enzyme Activation; D015870:Gene Expression; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials; D051379:Mice; D009419:Nerve Tissue Proteins; D018408:Patch-Clamp Techniques; D010903:Pituitary Gland, Anterior / Q000502:physiology*; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D015221:Potassium Channels; D011493:Protein Kinase C; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism; D013873:Thionucleotides / Q000494:pharmacology
D002712:Chlorides; D054815:Cyclic Nucleotide-Gated Cation Channels; C578666:Hcn1 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D013873:Thionucleotides; D002586:Cesium; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000324:Adrenocorticotropic Hormone; D012964:Sodium; D000242:Cyclic AMP; D011493:Protein Kinase C; C028019:cesium chloride; D011188:Potassium