K. Haverkampf et al., THERMODYNAMICALLY SPECIFIC GATING KINETICS OF CARDIAC MAMMALIAN K-ATP(-DEGREES-C() CHANNELS IN A PHYSIOLOGICAL ENVIRONMENT NEAR 37), The Journal of membrane biology, 146(1), 1995, pp. 85-90
Elementary K+ currents through isolated ATP-sensitive K+ channels from
neonatal rat cardiocytes were recorded to study their temperature dep
endence between 9 degrees C and 39 degrees C. Elementary current size
and, thus, K+ permeation through the open pore varied monotonically wi
th temperature with a Q(10) of 1.25 corresponding to a low activation
energy of 3.9 kcal/mol. Open-state kinetics showed a complicated tempe
rature dependence with Q(10) values of up to 2.94. Arrhenius anomalies
of tau(open(1)) and tau(open(2)) indicate the occurrence of thermally
-induced perturbations with a dominating influence on channel portions
that are involved in gating but are obviously ineffective in altering
pore-forming segments. At 39 degrees C, open-state exit reactions wer
e associated with the highest activation energy (O-2 exit reaction: 12
.1 kcal/ mel) and the largest amount of entropy. A transition from 19
degrees C to 9 degrees C elucidated a paradoxical kinetic response, sh
ortening of both O-states, irrespective of the absence or presence of
cAMP-dependent phosphorylation. Another member of the K+ channel famil
y and also a constituent of neonatal rat cardiocyte membranes, 66 pS o
utwardly-rectifying channels, was found to react predictably since tau
(open) increased on cooling. Obviously, cardiac K-(ATP(+)) channels do
not share this exceptional kinetic responsiveness to a temperature tr
ansition from 19 degrees C to 9 degrees C with other K+ channels and h
ave a unique sensitivity to thermally-induced perturbations.