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Early regulation of membrane excitability by ras oncogene proteins
C Collin1, A G Papageorge, M Sakakibara
1National Institutes of Health, Laboratory of Molecular and Cellular Neurobiology, Bethesda, Maryland 20892.
Abstract:
Two electrode voltage clamp conditions were used to study the early effects on ionic membrane channels of the intracellularly injected proto-oncogenic form of c-Ha-ras (c-ras) and its oncogenic counterpart v-Ha-ras (v-ras). These experiments were conducted on isolated somata of identified fully differentiated neurons of the sea snail Hermissenda. 20 min after c-ras, and 10 min after v-ras intracellular injections into type B medial photoreceptors of Hermissenda, the peak amplitude of two outward potassium currents (IA and IC), across the isolated Type B soma membrane begin to decrease. These two currents have been previously isolated by differences in activation and inactivation kinetics and their response to pharmacological blockers. c- or v-ras injections did not have any effect on a voltage-dependent inward calcium current. Reduction of IA preceded that of IC. Current reductions due to c-ras, but not to v-ras injection reversed spontaneously after 40 min. The voltage dependence of the steady state inactivation of IA shifted toward more negative potentials with ras injections. Ras-mediated cell transformations therefore, could involve, perhaps as initial events, prolonged modification of membrane currents.
Insights
Intracellular injection of ras oncogenes into Hermissenda neurons altered ionic membrane channel activity. These ras proteins reduced outward potassium currents (IA and IC), suggesting a role in cell transformation.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Proto-oncogenes like c-Ha-ras and oncogenes like v-Ha-ras play critical roles in cell signaling and transformation.
- Ionic membrane channels are crucial for neuronal function, regulating electrical excitability.
- Understanding the early effects of ras proteins on neuronal ion channels is key to deciphering their role in cell transformation.
Purpose of the Study:
- To investigate the early effects of intracellularly injected c-Ha-ras and v-Ha-ras on ionic membrane channels in differentiated neurons.
- To determine if ras proteins directly modulate specific ion currents and their properties.
Main Methods:
- Utilized two-electrode voltage clamp techniques on isolated somata of Hermissenda type B medial photoreceptors.
- Studied the effects of intracellular injection of c-Ha-ras and v-Ha-ras on voltage-dependent ionic currents.
- Differentiated and isolated specific outward potassium currents (IA and IC) and inward calcium currents.
Main Results:
- Intracellular injection of c-ras and v-ras led to a decrease in the peak amplitude of outward potassium currents IA and IC.
- The reduction in IA preceded the reduction in IC.
- No significant effect was observed on the voltage-dependent inward calcium current.
- Current reductions induced by c-ras reversed spontaneously after 40 minutes, while v-ras effects did not.
- Ras injections shifted the voltage dependence of steady-state inactivation of IA towards more negative potentials.
Conclusions:
- Ras proteins can rapidly and profoundly modify neuronal membrane ionic currents.
- These modifications, particularly to potassium currents, may represent early events in ras-mediated cell transformation.
- The differential reversibility of c-ras and v-ras effects suggests distinct mechanisms or downstream consequences.