title: Whole-cell and single-channel analysis of P-type calcium currents in cerebellar Purkinje cells of leaner mutant mice.
abstract: The leaner (tgla) mutation in mice results in severe ataxia and an overt neurodegeneration of the cerebellum. Positional cloning has revealed that the tgla mutation occurs in a gene encoding the voltage-activated calcium channel alpha1A subunit. The alpha1A subunit is highly expressed in the cerebellum and is thought to be the pore-forming subunit of P- and Q-type calcium channels. In this study we used both whole-cell and single-channel patch-clamp recordings to examine the functional consequences of the tgla mutation on P-type calcium currents. High-voltage-activated (HVA) calcium currents were recorded from acutely dissociated cerebellar Purkinje cells of homozygous leaner (tgla/tgla) and age-matched wild-type (+/+) mice. In whole cell recordings, we observed a marked reduction of peak current density in tgla/tgla Purkinje cells (-35.0 +/- 1.8 pA/pF) relative to that in +/+ (-103.1 +/- 5.9 pA/pF). The reduced whole-cell current in tgla/tgla cells was accompanied by little to no alteration in the voltage dependence of channel gating. In both genotypes, HVA currents were predominantly of the omega-agatoxin-IVA-sensitive P-type. Cell-attached patch-clamp recordings revealed no differences in single-channel conductance between the two genotypes and confirmed the presence of three distinct conductance levels (9, 13-14, and 17-18 pS) in cerebellar Purkinje cells. Analysis of patch open-probability (NPo) revealed a threefold reduction in the open-probability of channels in tgla/tgla patches (0.04 +/- 0.01) relative to that in +/+ (0.13 +/- 0.02), which may account for the reduced whole-cell current in tgla/tgla Purkinje cells. These results suggest that the tgla mutation can alter native P-type calcium channels at the single-channel level and that these alterations may contribute to the neuropathology of the leaner phenotype.
authors.affiliation: Department of Medical Pharmacology and Toxicology, College of Medicine, Texas A&M University Health Science Center, College Station, Texas 77843-1114, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Dove
authors.forename: L C
authors.initials: LC
authors.lastname: Abbott
authors.forename: W H
authors.initials: WH
authors.lastname: Griffith
mesh_terms: D000818:Animals; D001835:Body Weight / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000235:genetics* / Q000378:metabolism*; D020864:Calcium Channels, N-Type; D004553:Electric Conductivity; D004558:Electric Stimulation; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008818:Mice, Neurologic Mutants; D009154:Mutation / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011336:Probability; D011689:Purkinje Cells / Q000737:chemistry* / Q000502:physiology*; D013111:Spider Venoms / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020864:Calcium Channels, N-Type; D009543:Nifedipine; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA