Altered Calcium Homeostasis in Cerebellar Purkinje Cells of Leaner Mutant Mice

• Published in: Journal of neurophysiology Vol. 84; no. 1; pp. 513 - 524
• Main Authors: Dove, Leonard S, Nahm, Sang-Soep, Murchison, David, Abbott, Louise C, Griffith, William H
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.07.2000
• Subjects: Animals; Body Weight - genetics; Buffers; Calbindin 1; Calbindins; Calcium - metabolism; Calcium-Transporting ATPases - antagonists & inhibitors; Calcium-Transporting ATPases - metabolism; Endoplasmic Reticulum - enzymology; Enzyme Inhibitors - pharmacology; Female; Gene Expression - physiology; Heterozygote; Homeostasis - physiology; Homozygote; Male; Membrane Potentials - drug effects; Membrane Potentials - physiology; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Parvalbumins - genetics; Parvalbumins - metabolism; Patch-Clamp Techniques; Phenotype; Purkinje Cells - metabolism; RNA, Messenger - analysis; S100 Calcium Binding Protein G - genetics; S100 Calcium Binding Protein G - metabolism; thapsigargin; Thapsigargin - pharmacology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2000.84.1.513

  1 Department of Medical Pharmacology and Toxicology, College of Medicine, Texas A&M University System Health Science Center, College Station 77843-1114; and   2 Department of Veterinary Anatomy and Public Health, College of Veterinary Medicine, Texas A&M University, College Station, Texas 77843-4458 Dove, Leonard S., Sang-Soep Nahm, David Murchison, Louise C. Abbott, and William H. Griffith. Altered Calcium Homeostasis in Cerebellar Purkinje Cells of Leaner Mutant Mice. J. Neurophysiol. 84: 513-524, 2000. The leaner (tg la ) mouse mutation occurs in the gene encoding the voltage-activated Ca 2+ channel 1A subunit, the pore-forming subunit of P/Q-type Ca 2+ channels. This mutation results in dramatic reductions in P-type Ca 2+ channel function in cerebellar Purkinje neurons of tg la /tg la mice that could affect intracellular Ca 2+ signaling. We combined whole cell patch-clamp electrophysiology with fura-2 microfluorimetry to examine aspects of Ca 2+ homeostasis in acutely dissociated tg la /tg la Purkinje cells. There was no difference between resting somatic Ca 2+ concentrations in tg la /tg la cells and in wild-type (+/+) cells. However, by quantifying the relationship between intracellular Ca 2+ elevations and depolarization-induced Ca 2+ influx, we detected marked alterations in rapid calcium buffering between the two genotypes. Calcium buffering values (ratio of bound/free ions) were significantly reduced in tg la /tg la (584 ± 52) Purkinje cells relative to +/+ (1,221 ± 80) cells. By blocking the endoplasmic reticulum (ER) Ca 2+ -ATPases with thapsigargin, we observed that the ER had a profound impact on rapid Ca 2+ buffering that was also differential between tg la /tg la and +/+ Purkinje cells. Diminished Ca 2+ uptake by the ER apparently contributes to the reduced buffering ability of mutant cells. This report constitutes one of the few instances in which the ER has been implicated in rapid Ca 2+ buffering. Concomitant with this reduced buffering, in situ hybridization with calbindin D28k and parvalbumin antisense oligonucleotides revealed significant reductions in mRNA levels for these Ca 2+ -binding proteins (CaBPs) in tg la /tg la Purkinje cells. All of these results suggest that alterations of Ca 2+ homeostasis in tg la /tg la mouse Purkinje cells may serve as a mechanism whereby reduced P-type Ca 2+ channel function contributes to the mutant phenotype.