TEMPORAL REGULATION OF SHAKER-LIKE AND SHAB-LIKE POTASSIUM CHANNEL GENE-EXPRESSION IN SINGLE EMBRYONIC SPINAL NEURONS DURING K+ CURRENT DEVELOPMENT

A developmental increase in density of delayed rectifier potassium cur rent (I-Kv) in embryonic Xenopus spinal neurons shortens action potent ial durations and limits calcium influx governing neuronal differentia tion. Although previous work demonstrates that maturation of I-Kv depe nds on general mRNA synthesis, it is not known whether increases in K channel gene transcripts direct maturation of the current. Accordingl y, the developmental appearance of specific Kv potassium channel genes was determined using single-cell reverse transcription-PCR techniques after whole-cell recording of I-Kv during the period of its developme nt. Detection of a coexpressed housekeeping gene along with the potass ium channel gene controlled for successful aspiration of cellular mRNA and allowed scoring of cells in which Kv gene transcripts were not de tected. Diverse types of Xenopus spinal neurons exhibit homogenous dev elopment of I-Kv both in vivo and in culture, In contrast, transcripts of two genes encoding delayed rectifier current, Kv1.1 (Shaker) and K v2.2 (Shab), are expressed heterogeneously during the period in which the current develops. Kv1.1 mRNA achieves maximal appearance in simila r to 30% of cells, while I-Kv is immature; Kv2.2 mRNA appears later in similar to 60% of mature neurons. Kv1.1 and 2.2 are thus candidates f or generation of I-Kv, and spinal neurons are a heterogeneous populati on with respect to potassium channel gene expression. Moreover, correl ation of gene expression with current properties shows that neurons la cking Kv2.2 have a characteristic voltage dependence of activation of I-Kv.