Regulation Of Neuronal Excitability: New Mechanisms For Slow Afterhyperpolarization Activation And Modulation

<p>One of the most characteristic features of pyramidal cells in the prefrontal cortex (PFC) is that they present a slow afterhyperpolarizing current (I_sAHP) that plays a critical role in the regulation of neuronal excitability. This current is modulated by receptors acting via GΑ_q/11 G proteins, thus it is thought that neurotransmitters regulate neuronal excitability through the inhibition of this current. I_sAHP is known to be mediated by calcium-activated potassium channels, however, neither the identity of the channel underlying this current nor its mechanism of activation are yet well understood. Recent reports have questioned a direct role of calcium in the activation of the channels underlying the I_sAHP in hippocampus, suggesting the neuronal calcium sensor (NCS) protein hippocalcin as one of the plausible proteins involved in the triggering of I_sAHP; therefore, one of the aims of this work will be to examine the role of hippocalcin and other NCS proteins in the development of I_sAHP in pyramidal neurons of the PFC.</p> <p>In the present study we used loss of function and overexpression techniques to demonstrate that hippocalcin is an important component in the development of the I_sAHP in pyramidal neurons of the prefrontal cortex. Furthermore, we also established that neurocalcin-Δ, a close related member of the visinin-like protein subfamily, but not VILIP-2 produced similar effects on I_sAHP. Transfection with either hippocalcin or neurocalcin- also altered the kinetic of I_sAHP reducing its rate of decay.</p> <p>Another characteristic feature of I_sAHP is that it runs down upon prolonged whole-cell recordings. This rundown was reduced when a precursor of PtdIns(4,5)P₂ was added to the recording pipette. Furthermore, blocking the resynthesis of PtdIns(4,5)P₂, greatly increased the rate of IsAHP rundown. Reducing PtdIns(4,5)P₂ levels or its availability at the plasma membrane greatly reduced I_sAHP amplitude highlighting the relevance of this phospholipids in the developing of I_sAHP. On the other hand, increasing PtdIns(4,5)P₂ levels at the plasma membrane, by expressing its synthetic enzyme (PIPK5), did not significantly increased I_sAHP amplitude, but strongly increased its sensibility to activation by calcium, thus ruling out a direct role of PtdIns(4,5)P₂ on activating I_sAHP in pyramidal neurons of the prefrontal cortex. These results propose the idea of an concerted mechanism of I_sAHP activation between calcium influx and PtdIns(4,5)P₂ availability at the plasma membrane and present I_sAHP not as a single unitary current, but rather as the embodiment of a biochemical gating mode.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Open Access Dissertation

Discipline thesis:degree_discipline

Pharmacology

Year dc:date.available

2010

Author dc:creator

• Villalobos, Claudio Alberto

Contributors dc:contributor

• RODRIGO ANDRADE

• G protein-coupled receptors
• hippocalcin
• neuronal excitability
• phosphatidylinositol (4
• 5)bisphosphate
• prefrontal cortex
• slow afterhyperpolarization
• Neurosciences

Repository record dc:identifier

https://digitalcommons.wayne.edu/oa_dissertations/190

OAI identifier oai:identifier

oai:digitalcommons.wayne.edu:oa_dissertations-1189