Cultured oligodendrocytes (OLGs) are capable of forming myeline-like structures in the absence of neurons or other cell types. However, there is mounting evidence to suggest that local axo-glial modulatory signals may play a role in regulating myelination. Adult OLGs in pure culture express predominantly K+ channels. OLGs also express B-adrenergic receptors and prostaglandin receptors, but lack other neuroligand receptors as have been demonstrated in cultured astrocytes (some of which are linked with intracellular Ca++ mobilization or Ca++ influx). It is possible that the presence of other central nervous system (CNS) cell types may alter the expression of ion channels and neuroligand receptors that could play an important role in neuron-glia signalling. A disturbance in neuron-glia signalling may contribute to failure of remyelination in multiple sclerosis. The proposed investigation is aimed at elucidating the interaction between OLGs with other CNS cell types. We will examine the possibility that the expression of channels other than K+, e.g. voltage-gated Ca++ channels and glutamate channels may be induced when cultured OLGs are grown in the presence of neurons. We will employ patch-clamp techniques as well as image and photometric analysis of intracellular Ca++ transients to study the expression of ion channels and neuroligand receptors in OLGs grown in neuronal conditioned media, as well s in OLGs grown in mixed culture. We will pursue the link between modulation of K+ channels and myelin formation. We will study the effect of high external K+ and K+ channel blockers on the synthesis and phosphorylation of the major structural protein of myeline i.e. myelin basic protein in purified OLG cultures as well as in co-cultures. The primary genetic deficit in dysmyelinating mouse mutants prevents the synthesis of a major structural protein in myelin. We will examine the electrophysiologic properties of OLGs isolated from dysmyelinating mutants. If K+ outward currents of OLGs from these mutants are abnormal, we will attempt to transiently express isoforms of mammalian K+ channels from mRNA generated from complete cDNA clones to determine whether altered ion channel expression can be linked to restoration of function i.e. synthesis of myelin. If the inwardly rectifying K+ current from the abnormal OLGs is affected as opposed to the outwardly rectifying K+ current, we will attempt to clone the inwardly rectifying K+ channel as we have done for the delayed rectifier and neuronal A-like channels and transvect the abnormal OLGs with the cloned inwardly rectifying channel. These studies will contribute to our understanding of neuron-glia signalling, glial regulation of ion channel expression, and the role of ion channels in the control of myelin biosynthetic pathways.
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