Temperature-sensitive gating of cation current in guinea pig ileal muscle activated by hyperpolarization.
The temperature dependence of hyperpolarization-activated current (I(h)) was investigated in freshly isolated guinea pig ileal smooth muscle cells, using the nystatin-perforated whole cell recording technique. Hyperpolarizing pulses (-50 to -120 mV) from -40 mV evoked time-dependent inward rectifying currents with a reversal potential of -33 mV and a slow activation time course well approximated by a single exponential. The properties of these currents, such as steady-state variables, dependence on external K, modification by norepinephrine, and blockade by Cs or ZD-7288, coincide well with those of the "classical" I(h) discovered in the sinoatrial node. Raising the temperature (range: 22-33 degrees C) accelerated the activation time course of this I(h) and shifted its 50% activation potential positively (12 mV/10 degree) with much less change in the maximum conductance. Based on a simple closed-open model, this can be explained by a high temperature dependence of the opening rate constant (temperature coefficient: 3.4). The activation profile of reconstructed I(h) at 36 degrees C suggests that a considerable overlap could occur between the ranges of I(h) activation and physiological membrane potential.
Yanagida
H
H
Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Inoue
R
R
Tanaka
M
M
Ito
Y
Y
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D005260:Female; D005769:Gastrointestinal Motility / Q000502:physiology*; D006168:Guinea Pigs; D007082:Ileum / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D013696:Temperature; D019789:Tetraethylammonium / Q000494:pharmacology
D002316:Cardiotonic Agents; D002412:Cations; D007473:Ion Channels; D010726:Phosphodiesterase Inhibitors; D011743:Pyrimidines; D013566:Sympathomimetics; C082246:ICI D2788; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D015056:1-Methyl-3-isobutylxanthine; D009638:Norepinephrine