Bilirubin augments Ca2+ load of developing bushy neurons by targeting specific subtype of voltage-gated calcium channels

Sci Rep. 2017 Mar 27;7(1):431. doi: 10.1038/s41598-017-00275-9.

Abstract

Neonatal brain is particularly vulnerable to pathological levels of bilirubin which elevates and overloads intracellular Ca2+, leading to neurotoxicity. However, how voltage-gated calcium channels (VGCCs) are functionally involved in excess calcium influx remains unknown. By performing voltage-clamp recordings from bushy cells in the ventral cochlear nucleus (VCN) in postnatal rat pups (P4-17), we found the total calcium current density was more than doubled over P4-17, but the relative weight of VGCC subtypes changed dramatically, being relatively equal among T, L, N, P/Q and R-type at P4-6 to predominantly L, N, R over T and P/Q at P15-17. Surprisingly, acute administration of bilirubin augmented the VGCC currents specifically mediated by high voltage-activated (HVA) P/Q-type calcium currents. This augment was attenuated by intracellular loading of Ca2+ buffer EGTA or calmodulin inhibitory peptide. Our findings indicate that acute exposure to bilirubin increases VGCC currents, primarily by targeting P/Q-type calcium channels via Ca2+ and calmodulin dependent mechanisms to overwhelm neurons with excessive Ca2+. Since P/Q-subtype calcium channels are more prominent in neonatal neurons (e.g. P4-6) than later stages, we suggest this subtype-specific enhancement of P/Q-type Ca2+ currents likely contributes to the early neuronal vulnerability to hyperbilirubinemia in auditory and other brain regions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Newborn
  • Bilirubin / metabolism*
  • Calcium / metabolism*
  • Calcium Channels / metabolism*
  • Cells, Cultured
  • Neurons / drug effects*
  • Neurons / physiology*
  • Patch-Clamp Techniques
  • Rats

Substances

  • Calcium Channels
  • Bilirubin
  • Calcium