Hypokalaemic periodic paralysis (HypoPP) is an autosomal dominant muscle disease which has been linked to point mutations in the skeletal muscle L-type calcium channel cq subunit (~ls). Here, we have introduced one of the point mutations causing HypoPP (R528H) into cDNA of the rabbit Cqs. Expression of either the wild-type ~tsor the mutant R528H Cqs (~ls-Rszsn) subunits was obtained in mouse Ltk cells using a selectable expression vector. The Cqs-Rs28n subunit led to the expression of functional L-type Ca z+ channels. Corresponding whole-cell Ba 2+ currents exhibit very slow activation and inactivation kinetics, typical for recombinant skeletal Ca 2+ channel currents. Voltage-dependent activation and inactivation properties were similar for ~ts-and ~IS-RS2Sn, as well as their sensitivity to the dihydropyridine agonist Bay K 8644. Differences in Cqs-and ~ls-Rs28n-directed channels reside in the Ba 2+ current density, which was significantly reduced 3.2 fold in cells expressing ~lS-RS2Sn It was concluded that the R528H mutation of Cqs results in minor differences in the electrophysiological properties but significantly reduces the whole-cell Ca z÷ channel current in its amplitude.

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Cross-transplantations of neural tissue have been performed between jimpy (jp), shiverer (shi), and normal mice. Taking advantage of the absence of immunodetectable myelin basic protein (MBP) in the shi brain, jp myelin has been identified in the shi recipient by using an anti-MBP antiserum. By contrast, shi as well as normal myelin have been identified in the jp brain by using an anti-C-terminal hexapeptide of the proteolipid protein (PLP) (this PLP hexapeptide being absent in the jp PLP). When transplanted under homochronic conditions (newborn into newborn), jp oligodendrocytes (ODC) express their usual phenotype in a normal or a shi environment, suggesting that at birth the jp ODCs phenotype is strictly established and cannot be modified by environmental conditions. The reverse transplantations (newborn shi or normal into newborn jp brain) demonstrate that the jp environment does not modify the phenotype of normal or shi ODCs. Finally, these experiments demonstrated a normal timing of differentiation of jp axons and of jp ODCs.