Regulation of Ca²⁺-Dependent K⁺Channel Expression in Rat Cerebellum during Postnatal Development

Abstract

Potassium channels govern duration and frequency of excitable membrane events and may regulate signals that are important in neuronal development. This study assesses the developmental expression of the large conductance Ca2+-dependent K+ channel in vivo and in vitro in rat cerebellum. In vivo, transcript levels for the Ca2+-dependent K+ channel (KCa) were shown by Northern analysis to increase during development, whereas transcript levels for the voltage-gated K+ channel Kv3.1, a delayed rectifier (KD), remained relatively constant. A comparable pattern was demonstrated by expression in Xenopus oocytes of poly(A)-enriched RNA isolated from postnatal rat cerebella. In cerebellar cultures, increased external K+ provided a simple manipulation of cell excitability that influenced KCa transcript levels during development. With low external K+ (5.3 mM), the levels of KCa channel transcript (assessed by semiquantitative PCR) remained constant throughout development. However, in culture medium that supported significant dendritic outgrowth (10 mM extracellular K+), an upregulation of KCa transcript level was observed similar to that seen in vivo. Tetraethylammonium (TEA; 1 mM) similarly enhanced KCa expression, suggesting that depolarizing stimuli increased KCa expression. The stimulatory effects of increased K+ or TEA on KCa expression required extracellular Ca2+ and were abolished in low external calcium (0.1 mM, buffered with EGTA), although morphological development and survival were not impaired. The regulation of KCa channel expression by depolarization and Ca2+ entry provides evidence of a logical feedback mechanism governing Ca2+ signals that may be significant in cerebellar development.

Down-regulation of BK channel expression in the pilocarpine model of temporal lobe epilepsy

“…To discern changes in expression levels, the number of PCR cycles was adjusted so that both signals would be amplified within the exponential phase of the reaction as previously determined (not shown). The primers to amplify rat BK transcripts have been previously characterized and yield a 312 bp product (Muller et al, 1998). Semi-quantitative RT-PCR assays revealed that expression of BK channel transcripts was significantly decreased at 30 cycles (31.1±3.5% reduction of controls, P<0.01, Paired t-test, n=4) (Fig.…”

“…Specific primers for the rat BK channel related sequences were sense 5′-GGCTGGAAGTGAATTCTGTAG-3′ and antisense 5′-TGAGTAAGTAGACACATTCCC-3′. These primer sequences are based on the rat brain BK channel sequence rslo in regions that correspond in mslo to 1063-1083 bases and produced a product of 312 base pairs (bp) as reported before (Muller et al, 1998). Housekeeping gene for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) served as an internal control and ran parallel in separate reaction tubes for the semi-quantitative relative comparison purposes.…”

Ion Channel Development, Spontaneous Activity, and Activity-Dependent Development in Nerve and Muscle Cells

“…Cerebellar Purkinje neurons, for example, are spontaneously active in both the immature and mature states, but the pattern of activity changes from steady firing to more bursting behavior. It is likely that activity-dependent developmental expression of a Ca 2ϩ -activated K ϩ channel participates in this transition as well (433). I K(Ca) development also depends on early periods of spontaneous activity in mammalian spinal motor neurons (378), although its role in terminating or modifying the activity is not yet understood.…”

Decline in Glucokinase Activity in the Arcuate Nucleus of Streptozotocin-Induced Diabetic Rats

“…lateral hypothalamic area (LHA), ventromedial nucleus (VMN), paraventricular nucleus (PVN), dorsomedial nucleus (DMN), and arcuate nucleus (ARN), by use of the in situ hybridization technique. [6][7][8] The GK mRNA-expressing areas in the hypothalamus are considered to contain glucose-sensitive or glucose-responsive cells [9][10][11] and to play roles in feeding behavior and glucose homeostasis. [12][13][14] GK immunoreactivity is also localized in the ependymocytes lining the ventricles and serotonin neurons in the midline medulla.…”