Dataset Information

Inwardly permeating Na ions generate the voltage dependence of resurgent Na current in cerebellar Purkinje neurons.

ABSTRACT: Voltage-gated Na channels of cerebellar Purkinje neurons express an endogenous open-channel blocking protein. This blocker binds channels at positive potentials and unbinds at negative potentials, generating a resurgent Na current and permitting rapid firing. The macroscopic voltage dependence of resurgent current raises the question of whether the blocker directly senses membrane potential or whether voltage dependence is conferred indirectly. Because we previously found that inwardly permeating Na ions facilitate dissociation of the blocker, we measured voltage-clamped currents in different Na gradients to test the role of permeating ions in generating the voltage dependence of unblock. In reverse gradients, outward resurgent currents were tiny or absent, suggesting that unblock normally requires "knockoff" by Na. Inward resurgent currents at strongly negative potentials, however, were larger in reverse than in control gradients. Moreover, occupancy of the blocked state was prolonged both in reverse gradients and in control gradients with reduced Na concentrations, indicating that block is more stable when inward currents are small. Accordingly, reverse gradients shifted the voltage dependence of block, such that resurgent currents were evoked even after conditioning at negative potentials. Additionally, in control gradients, peak resurgent currents decreased linearly with driving force during the conditioning step, suggesting that the stability of block varies directly with inward Na current amplitude. Thus, the voltage dependence of blocker unbinding results almost entirely from repulsion by Na ions occupying the external pore. The lack of voltage sensitivity of the blocking protein suggests that the blocker's binding site lies outside the membrane field, in the permeation pathway.

SUBMITTER: Aman TK

PROVIDER: S-EPMC2865843 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Inwardly permeating Na ions generate the voltage dependence of resurgent Na current in cerebellar Purkinje neurons.

Aman Teresa K TK Raman Indira M IM

The Journal of neuroscience : the official journal of the Society for Neuroscience 20100401 16

Voltage-gated Na channels of cerebellar Purkinje neurons express an endogenous open-channel blocking protein. This blocker binds channels at positive potentials and unbinds at negative potentials, generating a resurgent Na current and permitting rapid firing. The macroscopic voltage dependence of resurgent current raises the question of whether the blocker directly senses membrane potential or whether voltage dependence is conferred indirectly. Because we previously found that inwardly permeatin ...[more]

PMID: 20410115

Similar Datasets

Project description:Cardiac cells express more than one isoform of the Na, K-ATPase (NKA), the heteromeric enzyme that creates the Na(+) and K(+) gradients across the plasmalemma. Cardiac isozymes contain one catalytic ?-subunit isoform (?1, ?2, or ?3) associated with an auxiliary ?-subunit isoform (?1 or ?2). Past studies using biochemical approaches have revealed minor kinetic differences between isozymes formed by different ?-? isoform combinations; these results make it difficult to understand the physiological requirement for multiple isoforms. In intact cells, however, NKA enzymes operate in a more complex environment, which includes a substantial transmembrane potential. We evaluated the voltage dependence of human cardiac NKA isozymes expressed in Xenopus oocytes, and of native NKA isozymes in rat ventricular myocytes, using normal mammalian physiological concentrations of Na(+)o and K(+)o. We demonstrate that although ?1 and ?3 pumps are functional at all physiologically relevant voltages, ?2?1 pumps and ?2?2 pumps are inhibited by ?75% and ?95%, respectively, at resting membrane potentials, and only activate appreciably upon depolarization. Furthermore, phospholemman (FXYD1) inhibits pump function without significantly altering the pump's voltage dependence. Our observations provide a simple explanation for the physiological relevance of the ?2 subunit (?20% of total ? subunits in rat ventricle): they act as a reserve and are recruited into action for extra pumping during the long-lasting cardiac action potential, where most of the Na(+) entry occurs. This strong voltage dependence of ?2 pumps also helps explain how cardiotonic steroids, which block NKA pumps, can be a beneficial treatment for heart failure: by only inhibiting the ?2 pumps, they selectively reduce NKA activity during the cardiac action potential, leading to an increase in systolic Ca(2+), due to reduced extrusion through the Na/Ca exchanger, without affecting resting Na(+) and Ca(2+) concentrations.

Dataset Information

Inwardly permeating Na ions generate the voltage dependence of resurgent Na current in cerebellar Purkinje neurons.

Publications

Inwardly permeating Na ions generate the voltage dependence of resurgent Na current in cerebellar Purkinje neurons.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets