Temperature-sensitive activation of G-protein regulating the resting membrane conductance of Aplysia neurons.
Raising the temperature from 22 to 32 degrees C induced a marked hyperpolarization (15-30 mV) associated with an increase in membrane conductance of Aplysia neurons, whereas lowering the temperature from 22 to 12 degrees C caused a significant depolarization (10-20 mV) with a decrease in conductance. These temperature effects were far greater than those expected from the Nernst equation. The reversal potentials of these temperature responses corresponded with the equilibrium potential of K+, suggesting these responses were produced by opening or closing of K+ channels. Ouabain (5 x 10(-4) M) did not affect these temperature responses though it depolarized all cells examined (5-25 mV). Intracellularly injected guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) selectively depressed the response to warming without affecting the response to cooling. Intracellular application of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) produced a gradual increase in K+ conductance of the resting membrane and apparently depressed the response to warming while it markedly augmented the response to cooling. These results suggest that GTP binding protein can be activated thermally to open K+ channels without receptor stimulation. It is significant that the resting membrane potential of the neuron in the central nervous system may be regulated not only by Na+ pump but also by spontaneous activation of a certain GTP-binding protein, at least in Aplysia.
Hakozaki
S
S
Department of Physiology, School of Medicine, Iwate Medical University, Morioka, Japan.
Matsumoto
M
M
Sasaki
K
K
D000818:Animals; D001048:Aplysia / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D008564:Membrane Potentials; D009431:Neural Conduction; D009474:Neurons / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology; D013696:Temperature
D015221:Potassium Channels; D019204:GTP-Binding Proteins