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Jiang X, Shu HJ, Krishnan K, Qian M, Taylor AA, Covey DF, Zorumski CF, Mennerick S. A clickable neurosteroid photolabel reveals selective Golgi compartmentalization with preferential impact on proximal inhibition. Neuropharmacology 2016; 108:193-206. [PMID: 27114255 DOI: 10.1016/j.neuropharm.2016.04.031] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 03/18/2016] [Accepted: 04/21/2016] [Indexed: 11/18/2022]
Abstract
Anesthetic, GABA-active neurosteroids potently augment GABAA receptor function, leading to important behavioral consequences. Neurosteroids and their synthetic analogues are also models for a wide variety of cell-permeant neuroactive compounds. Cell permeation and compartmentalization raise the possibility that these compounds' actions are influenced by their cellular partitioning, but these contributions are not typically considered experimentally or therapeutically. To examine the interplay between cellular accumulation and pharmacodynamics of neurosteroids, we synthesized a novel chemical biology analogue (bio-active, clickable photolabel) of GABA-active neurosteroids. We discovered that the analogue selectively photo-labels neuronal Golgi in rat hippocampal neurons. The active analogue's selective distribution was distinct from endogenous cholesterol and not completely shared by some non-GABA active, neurosteroid-like analogues. On the other hand, the distribution was not enantioselective and did not require energy, in contrast to other recent precedents from the literature. We demonstrate that the soma-selective accumulation can act as a sink or source for steroid actions at plasma-membrane GABA receptors, altering steady-state and time course of effects at somatic GABAA receptors relative to dendritic receptors. Our results suggest a novel mechanism for compartment-selective drug actions at plasma-membrane receptors.
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Affiliation(s)
- Xiaoping Jiang
- Departments of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Hong-Jin Shu
- Departments of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Kathiresan Krishnan
- Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Mingxing Qian
- Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Amanda A Taylor
- Departments of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Douglas F Covey
- Developmental Biology, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA; Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA; Taylor Family Institute for Innovative Psychiatry Research, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Charles F Zorumski
- Departments of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA; Neuroscience, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA; Taylor Family Institute for Innovative Psychiatry Research, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
| | - Steven Mennerick
- Departments of Psychiatry, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA; Neuroscience, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA; Taylor Family Institute for Innovative Psychiatry Research, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA.
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Abstract
Voltage-sensitive dyes are important tools for assessing network and single-cell excitability, but an untested premise in most cases is that the dyes do not interfere with the parameters (membrane potential, excitability) that they are designed to measure. We found that popular members of several different families of voltage-sensitive dyes modulate GABA(A) receptor with maximum efficacy and potency similar to clinically used GABA(A) receptor modulators. Di-4-ANEPPS and DiBAC4(3) potentiated GABA function with micromolar and high nanomolar potency, respectively, and yielded strong maximum effects similar to barbiturates and neurosteroids. Newer blue oxonols had biphasic effects on GABA(A) receptor function at nanomolar and micromolar concentrations, with maximum potentiation comparable to that of saturating benzodiazepine effects. ANNINE-6 and ANNINE-6plus had no detectable effect on GABA(A) receptor function. Even dyes with no activity on GABA(A) receptors at baseline induced photodynamic enhancement of GABA(A) receptors. The basal effects of dyes were sufficient to prolong IPSCs and to dampen network activity in multielectrode array recordings. Therefore, the dual effects of voltage-sensitive dyes on GABAergic inhibition require caution in dye use for studies of excitability and network activity.
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