Temporal regulation of Shaker- and Shab-like potassium channel gene expression in single embryonic spinal neurons during K+ current development

Abstract

A developmental increase in density of delayed rectifier potassium current (I(Kv)) in embryonic Xenopus spinal neurons shortens action potential durations and limits calcium influx governing neuronal differentiation. Although previous work demonstrates that maturation of I(Kv) depends on general mRNA synthesis, it is not known whether increases in K+ channel gene transcripts direct maturation of the current. Accordingly, 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 development. Detection of a coexpressed housekeeping gene along with the potassium channel gene controlled for successful aspiration of cellular mRNA and allowed scoring of cells in which Kv gene transcripts were not detected. Diverse types of Xenopus spinal neurons exhibit homogenous development of I(Kv) both in vivo and in culture. In contrast, transcripts of two genes encoding delayed rectifier current, Kv1.1 (Shaker) and Kv2.2 (Shab), are expressed heterogeneously during the period in which the current develops. Kv1.1 mRNA achieves maximal appearance in ~30% of cells, while I(Kv) is immature; Kv2.2 mRNA appears later in ~60% of mature neurons. Kv1.1 and 2.2 are thus candidates for generation of I(Kv), and spinal neurons are a heterogeneous population with respect to potassium channel gene expression. Moreover, correlation of gene expression with current properties shows that neurons lacking Kv2.2 have a characteristic voltage dependence of activation of I(Kv).