Pentobarbital inhibition of human recombinant α 1A P/Q-type voltage-gated calcium channels involves slow, open channel block

A. Schober, E. Sokolova, K. J. Gingrich

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Background and Purpose: Pre-synaptic neurotransmitter release is largely dependent on Ca 2+ entry through P/Q-type (Ca V2.1) voltage-gated Ca 2+ channels (PQCCs) at most mammalian, central, fast synapses. Barbiturates are clinical depressants and inhibit pre-synaptic Ca 2+ entry. PQCC barbiturate pharmacology is generally unclear, specifically in man. The pharmacology of the barbiturate pentobarbital (PB) in human recombinant α 1A PQCCs has been characterized. Experimental approach PB effects on macroscopic Ca 2+(I Ca) and Ba 2+(I Ba) currents were studied using whole-cell patch clamp recording in HEK-293 cells heterologously expressing (α 1A) human2aα 2δ-1) rabbit PQCCs. Key results: PB reversibly depressed peak current (I peak) and enhanced apparent inactivation (fractional current at 800 ms, r 800) in a concentration-dependent fashion irrespective of charge carrier (50% inhibitory concentration: I peak, 656 M; r 800, 104 M). Rate of mono-exponential I Ba decay was linearly dependent on PB concentration. PB reduced channel availability by deepening non-steady-state inactivation curves without altering voltage dependence, slowed recovery from activity-induced unavailable states and produced use-dependent block. PB (100 M) induced use-dependent block during physiological, high frequency pulse trains and overall depressed PQCC activity by two-fold. Conclusion and implications: The results support a PB pharmacological mechanism involving a modulated receptor with preferential slow, bimolecular, open channel block (K d = 15 M). Clinical PB concentrations (<200 M) inhibit PQCC during high frequency activation that reduces computed neurotransmitter release by 16-fold and is comparable to the magnitude of Ca 2+-dependent facilitation, G-protein modulation and intrinsic inactivation that play critical roles in PQCC modulation underlying synaptic plasticity. The results are consistent with the hypothesis that PB inhibition of PQCCs contributes to central nervous system depression underlying anticonvulsant therapy and general anaesthesia.

Original languageEnglish (US)
Pages (from-to)365-383
Number of pages19
JournalBritish Journal of Pharmacology
Volume161
Issue number2
DOIs
StatePublished - Sep 2010

Keywords

  • Ca 2.1
  • P/Q Ca channels
  • electrophysiology
  • pentobarbital
  • pharmacology
  • recombinant proteins

ASJC Scopus subject areas

  • Pharmacology

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