Merits and Limitations of Studying Neuronal Depolarization-Dependent Processes Using Elevated External Potassium

Abstract

Elevated extracellular potassium chloride is widely used to achieve membrane depolarization of cultured neurons. This technique has illuminated mechanisms of calcium influx through L-type voltage sensitive calcium channels, activity-regulated signaling, downstream transcriptional events, and many other intracellular responses to depolarization. However, there is enormous variability in these treatments, including durations from seconds to days and concentrations from 3mM to 150 mM KCl. Differential effects of these variable protocols on neuronal activity and transcriptional programs are underexplored. Furthermore, potassium chloride treatments in vitro are criticized for being poor representatives of in vivo phenomena and are questioned for their effects on cell viability. In this review, we discuss the intracellular consequences of elevated extracellular potassium chloride treatment in vitro, the variability of such treatments in the literature, the strengths and limitations of this tool, and relevance of these studies to brain functions and dysfunctions.

Keywords: L-type voltage sensitive calcium channels; extracellular potassium; immediate early genes (IEG); intracellular calcium; transcription.

Figure 1.

Neuronal Activity Under Elevated Extracellular KCl In Vitro. A: Spikes under KCl treatment as a % of baseline activity before treatment. Spiking is observed under 5mM KCl treatment, which matches [KCl] in standard media conditions, but disappears as [KCl]_o rises. Spike data were compared using ANOVA. *** P < 0.001. B: Example recordings during baseline measurements (top) and KCl treatments (bottom).

Figure 2.

CaMK, MAPK/ERK, and CaN Signaling From L-VSCCs to Transcription. Signaling pathways initiating from Ca²⁺ influx at L-type VSCCs leading to transcription in the nucleus. Solid arrows represent intra-somatic interactions. Dashed arrows represent translocation into the nucleus. Black arrows represent the CaMK pathway, orange arrows represent the MAPK/ERK pathway, and blue arrows represent the CaN pathway. Dephosphorylated CRTC1 (in dark blue) translocates into the nucleus, and phosphorylated CRTC1 (in light blue) moves out of the nucleus.