Substance P modulates calcium current in retinal bipolar neurons

Area of Science:

• Neuroscience
• Retinal Physiology
• Cellular Electrophysiology

Background:

• Retinal bipolar cells are crucial interneurons transmitting visual information from photoreceptors to ganglion cells.
• Amacrine cells provide extensive feedback to bipolar cells, utilizing various neurotransmitters, including neuropeptides like substance P.

Purpose of the Study:

• To investigate the electrophysiological effects of substance P on isolated goldfish retinal bipolar cells.
• To elucidate the role of substance P in modulating calcium currents within these neurons.

Main Methods:

• Isolation of single bipolar neurons from goldfish retina.
• Whole-cell patch-clamp recording to measure calcium currents.
• Application of substance P (0.1-1 nM) at varying membrane potentials.
• Investigation of the involvement of G-proteins using GTP and GDP-beta-S.

Main Results:

• Substance P induced a voltage-dependent inhibition of calcium current, most pronounced at negative potentials (-20 to -30 mV).
• The net effect of substance P was a depolarization shift in the voltage range for calcium current activation.
• The inhibitory effect was dependent on GTP and blocked by GDP-beta-S, indicating a G-protein mediated pathway.
• Somatostatin and metenkephalin produced similar modulations of calcium current.

Conclusions:

• Neuropeptides, such as substance P, somatostatin, and metenkephalin, modulate calcium currents in retinal bipolar cells via a G-protein signaling pathway.
• This modulation alters the voltage-dependence of calcium channel activation, potentially influencing visual signal processing in the retina.