Document Detail

Temperature dependence of macroscopic L-type calcium channel currents in single guinea pig ventricular myocytes.
MedLine Citation:
PMID:  8777479     Owner:  NLM     Status:  MEDLINE    
INTRODUCTION: Lowering temperature greatly reduces calcium influx through calcium channels. Studies on a number of tissues demonstrate that the peak inward current, ICa, exhibits Q10 values ranging from 1.8 to 3.5; however, it remains unclear which component(s) of calcium channel gating may give rise to this large temperature sensitivity. Components of gating that may affect channel availability include phosphorylation and changes in [Ca2+]i, processes that vary in pertinence depending on the channel examined. This study addresses this problem by examining the temperature sensitivity (from 34 degrees to 14 degrees C) of cardiac ICa under control conditions, during attenuation or activation of protein kinase A (PKA) activity, and when intracellular [Ca2+] has been elevated. METHODS AND RESULTS: ICa was studied using the whole cell configuration of the patch champ technique. In control, lowering temperature from 34 degrees to 24 degrees C resulted in a shift in the potential for maximum slope (Va) and the peak current (Ymax) toward more positive membrane potentials. The Q10 values for the decrease in Ymax and the macroscopic slope conductance (Gmax), which reflects the number of available channels, were 3.15 +/- 0.19 and 2.57 +/- 0.13, respectively. At 0 mV the Ca2+ current decayed biexponentially, and the two time constants (tau 1 and tau 2) showed Q10 values of 1.79 +/- 0.21 and 2.06 +/- 0.38, while their contribution to the total current (I1 and I2) showed a Q10 of 5.99 +/- 0.83 and 1.61 +/- 0.22. In myocytes loaded with inhibitors of the PKA cycle sufficient to inhibit the increase of ICa to 1 microM isoprenaline, the Q10 values for some of the kinetic parameters were increased with the Q10 for I1 increasing to 17.06 +/- 3.48. Stimulation of ICa by exposing myocytes to 1 microM isoprenaline reduced the temperature sensitivity of Ymax, Gmax and I1, yielding respective values of 2.00 +/- 0.18, 1.85 +/- 0.07, and 2.04 +/- 0.15. Raising [Ca2+]i to enhance Ca2+i-dependent inactivation, while affecting inactivation and activation kinetics, affected temperature sensitivity little compared to control. The Q10 for time to peak changed little under experimental conditions (2.3 to 2.4) CONCLUSIONS: Increasing the phosphorylated states of calcium channels, but not Ca2+i-dependent inactivation, reduces temperature sensitivity of certain gating parameters. The data suggest that the rate of the transitions between the unavailable and also between the various closed states are changed in the opposite direction to that induced by PKA-dependent phosphorylation. Processes, e.g., inhibitory mechanisms, may be involved to maintain channels in unavailable or "unphosphorylated" states, and it may be these that contribute to the high Q10 of macroscopic channel currents.
T J Allen
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of cardiovascular electrophysiology     Volume:  7     ISSN:  1045-3873     ISO Abbreviation:  J. Cardiovasc. Electrophysiol.     Publication Date:  1996 Apr 
Date Detail:
Created Date:  1996-09-19     Completed Date:  1996-09-19     Revised Date:  2010-03-24    
Medline Journal Info:
Nlm Unique ID:  9010756     Medline TA:  J Cardiovasc Electrophysiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  307-21     Citation Subset:  IM    
British Heart Foundation Research Group, Department of Physiology, School of Veterinary Science, Bristol, United Kingdom.
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MeSH Terms
Adrenergic beta-Agonists / pharmacology
Calcium / metabolism
Calcium Channels / physiology*
Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors,  metabolism
Guinea Pigs
Heart Ventricles / cytology,  enzymology,  metabolism
Membrane Potentials / drug effects,  physiology
Myocardium / cytology,  enzymology,  metabolism*
Patch-Clamp Techniques
Reg. No./Substance:
0/Adrenergic beta-Agonists; 0/Calcium Channels; 7440-70-2/Calcium; EC AMP-Dependent Protein Kinases

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