Inward rectifying currents stabilize the membrane potential in dendrites of mouse amacrine cells: patch-clamp recordings and single-cell RT-PCR.
OBJECTIVE
To explore the possible existence of inward rectifying currents in the distal dendrites of amacrine cells.


METHODS
Patch-clamp recordings were made from amacrine cells in a new horizontal slice preparation of mouse retina. Single-cell RT-PCR studies were performed after the patch-clamp recordings.


RESULTS
In contrast to results from vertical slices or dissociated cells, all amacrine cells tested demonstrated inward rectifying currents, IIR. Within the limits of our sample, this current did not depend on the morphological and physiological type of the amacrine cell. Amacrine cells from which the dendrites had been removed did not possess detectable amounts of IIR. Pharmacological experiments with ZD7288 (100 microM) and single-cell RT-PCR from recorded cells revealed that IIR includes an h-current (I(H)) carried by hyperpolarization-activated cyclic nucleotide gated channels (HCN), HCN1 and/or HCN2 subtypes. In the presence of extracellular Cs+ (5 mM), which greatly suppressed IIR, the resting membrane conductance was reduced. IIR suppressed the generation of oscillatory potentials. Intracellular cAMP (8-cpt-cAMP, 1 mM) activated IIR.


CONCLUSIONS
IIR appears to occur within dendrites of many amacrine cells, where it tends to stabilize the resting membrane potential. HCN1 and/or HCN2 channels contribute to IIR in amacrine cells. Dendritic IIR would be expected to contribute to functional independence of the distal dendrites of amacrine cells that express it.
Koizumi
Amane
A
Howard Hughes Medical Institute, Massachusetts General Hospital, Wellman 429, Boston, MA 02114, USA. akoizumi-ns@umin.ac.jp
Jakobs
Tatjana C
TC
Masland
Richard H
RH
D025042:Amacrine Cells / Q000502:physiology*; D000818:Animals; D002586:Cesium / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels; D003712:Dendrites / Q000502:physiology*; D004594:Electrophysiology; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009124:Muscle Proteins / Q000235:genetics / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013873:Thionucleotides / Q000494:pharmacology
D054815:Cyclic Nucleotide-Gated Cation Channels; C578666:Hcn1 protein, mouse; C578711:Hcn2 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D011743:Pyrimidines; D012333:RNA, Messenger; D013873:Thionucleotides; C082246:ICI D2788; D002586:Cesium; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000242:Cyclic AMP