Using Ca2+-channel biosensors to profile amphetamines and cathinones at monoamine transporters: electro-engineering cells to detect potential new psychoactive substances.

BACKGROUND

The appearance of stimulant-class new psychoactive substances (NPS) is a frequent and significant problem in our society. Cathinone variants are often sold illegally as 3,4-methylenedioxy methamphetamine ("ecstasy") or disguised for legal sale using misleading names such as "bath salts" and carry the risk of promoting disruptive mental states, addiction, and fatal overdose. The principal targets of these recreational drugs are monoamine transporters expressed in catecholaminergic and serotonergic neurons. Some transporter ligands can be transported into cells, where they can promote a massive release of neurotransmitters through reverse transport, and others can block uptake. A ligand's dopamine vs. serotonin transporter selectivity, potency, and activity as a substrate or blocker can help elucidate the abuse liability and subjective effects of a drug.

OBJECTIVES

Here, we describe the discovery, development, and validation of an emerging methodology for compound activity assessment at monoamine transporters.

KEY FINDINGS: Substrates generate inward electrical currents through transporters and can depolarize the plasma membrane, whereas blockers work as a "cork in a bottle" and function as antagonists. Voltage-gated Ca2+ channels were co-expressed with monoamine transporters in cultured cells and used to measure fluctuations of the membrane electrical potential. In this system, substrates of monoamine transporters produce reliable dose-dependent Ca2+ signals, while blockers hinder them.

DISCUSSION: This system constitutes a novel use of voltage-gated Ca2+ channels as biosensors for the purpose of characterizing ligand activity at monoamine transporters using fluorimetry. This approach in combination with in vivo evaluations of drugs' abuse-related effects is a powerful strategy for anticipating potential stimulant-class NPS.