ORIGINAL ARTICLE

Pflügers Archiv

, Volume 436, Issue 2, pp 238-247

Effects of temperature on human L-type cardiac Ca2+ channels expressed in Xenopus oocytes

  • T. J. A. AllenAffiliated withDepartment of Pharmacology, Royal Free Hospital School of Medicine, London, NW3 2PF, UK
  • , Gabor MikalaAffiliated withDepartment of Pharmacology, Royal Free Hospital School of Medicine, London, NW3 2PF, UK

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Abstract

 Temperature normally affects peak L-type Ca2+ channel (CaCh) current with a temperature coefficient (Q 10) of between 1.8 and 3.5; in cardiomyocytes attenuating protein kinase A activity increases Q 10 whilst activating it lowers Q 10. We examine temperature effects using cloned human cardiac CaChs expressed in Xenopus oocytes. Peak inward currents (I Ba) through expressed CaChs (i.e. α1Cα2aβ1b) exhibited a Q 10 of 5.8±0.4 when examined between 15 and 25°C. The nifedipine-sensitive I Ba exhibited a higher Q 10 of 8.7±0.5, whilst the nifedipine-insensitive I Ba exhibited Q 10 of 3.7±0.3. Current/voltage (I/V) relationships shifted to negative potentials on warming. Using instead a different CaCh β subunit isoform, β2c, gave rise to an I Ba similar to those expressed using β1b. We utilized a carboxyl deletion mutant, α1C-Δ1633, to determine the temperature sensitivity of the pore moiety in the absence of auxiliary subunits; I Ba through this channel exhibited a Q 10 of 9.3±0.3. However, the Q 10 for macroscopic conductance was reduced compared to that of heteromeric channels; decreasing from 5.0 (i.e. α1Cα2aβ1b) and 3.9 (i.e. α1Cα2aβ2c) to 2.4 (α1C-Δ1633). These observations differ markedly from those made in studies of cardiomyocytes, and suggest that enhanced sensitivity may depend on the membrane environment, channel assembly or other regulatory factors.

Key words Calcium Heart Hypothermia Phosphorylation Protein kinase A