ISSN:
1432-2013
Keywords:
Key words Calcium
;
Heart
;
Hypothermia
;
Phosphorylation
;
Protein kinase A
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
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. α1Cα2/δaβ1b) 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. α1Cα2/δaβ1b) and 3.9 (i.e. α1Cα2/δaβ2c) 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004240050628
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