ISSN:
1432-1424
Keywords:
K+ permeation
;
Open state kinetics
;
Q10
;
Arrhenius anomalies
;
Temperature dependence
;
cAMP-dependent phosphorylation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Elementary K+ currents through isolated ATP-sensitive K+ channels from neonatal rat cardiocytes were recorded to study their temperature dependence between 9°C and 39°C. Elementary current size and, thus, K+ permeation through the open pore varied monotonically with temperature with a Q10 of 1.25 corresponding to a low activation energy of 3.9 kcal/mol. Open-state kinetics showed a complicated temperature dependence with Q10 values of up to 2.94. Arrhenius anomalies of τopen(1) and τopen(2) indicate the occurrence of thermallyinduced perturbations with a dominating influence on channel portions that are involved in gating but are obviously ineffective in altering pore-forming segments. At 39°C, open-state exit reactions were associated with the highest activation energy (O2 exit reaction: 12.1 kcal/ mol) and the largest amount of entropy. A transition from 19°C to 9°C elucidated a paradoxical kinetic response, shortening of both O-states, irrespective of the absence or presence of cAMP-dependent phosphorylation. Another member of the K+ channel family and also a constituent of neonatal rat cardiocyte membranes, 66 pS outwardly-rectifying channels, was found to react predictably since τopen increased on cooling. Obviously, cardiac K (ATP) + channels do not share this exceptional kinetic responsiveness to a temperature transition from 19°C to 9°C with other K+ channels and have a unique sensitivity to thermally-induced perturbations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00232682
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