The Journal of Neurophysiology Vol. 84 No. 1 July 2000, pp. 513-524
Copyright ©2000 by the American Physiological Society

Altered Calcium Homeostasis in Cerebellar Purkinje Cells of Leaner Mutant Mice

 ¹Department of Medical Pharmacology and Toxicology, College of Medicine, Texas A&M University System Health Science Center, College Station 77843-1114; and  ²Department 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 Ca²⁺ channel _1A subunit, the pore-forming subunit of P/Q-type Ca²⁺ channels. This mutation results in dramatic reductions in P-type Ca²⁺ channel function in cerebellar Purkinje neurons of tg^la/tg^la mice that could affect intracellular Ca²⁺ signaling. We combined whole cell patch-clamp electrophysiology with fura-2 microfluorimetry to examine aspects of Ca²⁺ homeostasis in acutely dissociated tg^la/tg^la Purkinje cells. There was no difference between resting somatic Ca²⁺ concentrations in tg^la/tg^la cells and in wild-type (+/+) cells. However, by quantifying the relationship between intracellular Ca²⁺ elevations and depolarization-induced Ca²⁺ 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) Ca²⁺-ATPases with thapsigargin, we observed that the ER had a profound impact on rapid Ca²⁺ buffering that was also differential between tg^la/tg^la and +/+ Purkinje cells. Diminished Ca²⁺ 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 Ca²⁺ buffering. Concomitant with this reduced buffering, in situ hybridization with calbindin D28k and parvalbumin antisense oligonucleotides revealed significant reductions in mRNA levels for these Ca²⁺-binding proteins (CaBPs) in tg^la/tg^la Purkinje cells. All of these results suggest that alterations of Ca²⁺ homeostasis in tg^la/tg^la mouse Purkinje cells may serve as a mechanism whereby reduced P-type Ca²⁺ channel function contributes to the mutant phenotype.