Depressed excitability and ion currents linked to slow exocytotic fusion pore in chromaffin cells of the SOD1(G93A) mouse model of amyotrophic lateral sclerosis.

Abstract

Altered synaptic transmission with excess glutamate release has been implicated in the loss of motoneurons occurring in amyotrophic lateral sclerosis (ALS). Hyperexcitability or hypoexcitability of motoneurons from mice carrying the ALS mutation SOD1(G93A) (mSOD1) has also been reported. Here we have investigated the excitability, the ion currents, and the kinetics of the exocytotic fusion pore in chromaffin cells from postnatal day 90 to postnatal day 130 mSOD1 mice, when motor deficits are already established. With respect to wild-type (WT), mSOD1 chromaffin cells had a decrease in the following parameters: 95% in spontaneous action potentials, 70% in nicotinic current for acetylcholine (ACh), 35% in Na(+) current, 40% in Ca(2+)-dependent K(+) current, and 53% in voltage-dependent K(+) current. Ca(2+) current was increased by 37%, but the ACh-evoked elevation of cytosolic Ca(2+) was unchanged. Single exocytotic spike events triggered by ACh had the following differences (mSOD1 vs. WT): 36% lower rise rate, 60% higher decay time, 51% higher half-width, 13% lower amplitude, and 61% higher quantal size. The expression of the α3-subtype of nicotinic receptors and proteins of the exocytotic machinery was unchanged in the brain and adrenal medulla of mSOD1, with respect to WT mice. A slower fusion pore opening, expansion, and closure are likely linked to the pronounced reduction in cell excitability and in the ion currents driving action potentials in mSOD1, compared with WT chromaffin cells.

• Authors: Enrique Calvo-Gallardo, Ricardo de Pascual, José-Carlos Fernández-Morales, Juan-Alberto Arranz-Tagarro, Marcos Maroto, Carmen Nanclares, Luis Gandía, Antonio M G de Diego, Juan-Fernando Padín, Antonio G García
• Journal: American journal of physiology. Cell physiology (Am J Physiol Cell Physiol) Vol. 308 Issue 1 Pg. C1-19 (Jan 01 2015) ISSN: 1522-1563 [Electronic] United States
• PMID: 25377090 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 the American Physiological Society.

Chemical References

• Catecholamines
• Receptors, Nicotinic
• SOD1 protein, human
• nicotinic receptor subunit alpha3
• Sodium
• Sod1 protein, mouse
• Superoxide Dismutase
• Superoxide Dismutase-1
• Acetylcholine
• Potassium
• Calcium

Topics

• Acetylcholine (pharmacology)
• Action Potentials
• Age Factors
• Amyotrophic Lateral Sclerosis (enzymology, genetics, pathology, physiopathology)
• Animals
• Calcium (metabolism)
• Calcium Signaling
• Catecholamines (metabolism)
• Chromaffin Cells (drug effects, enzymology, metabolism)
• Disease Models, Animal
• Exocytosis (drug effects)
• Humans
• Ion Transport
• Kinetics
• Male
• Membrane Fusion (drug effects)
• Mice, Transgenic
• Motor Activity
• Motor Neurons (metabolism, pathology)
• Mutation
• Potassium (metabolism)
• Receptors, Nicotinic (drug effects, metabolism)
• Sodium (metabolism)
• Superoxide Dismutase (genetics, metabolism)
• Superoxide Dismutase-1
• Synaptic Transmission (drug effects)