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Kinetic Diversity of Single-Channel Burst Openings Underlying Persistent Na⁺ Current in Entorhinal Cortex Neurons

Jacopo Magistretti ^*, David S. Ragsdale  and Angel Alonso 

^* Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari, Università degli Studi di Pavia, Pavia, Italy, and Department of Neurology and Neurosurgery, McGill University and Montreal Neurological Institute, Montréal, Québec, Canada

Correspondence: Address reprint requests to Dr. Jacopo Magistretti, Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari, Sezione di Fisiologia Generale e Biofisica Cellulare, Università degli Studi di Pavia, Via Forlanini 6, 27100 Pavia, Italy. Tel.: 39-0382-507613 or 507857; Fax: 39-0382-507527; E-mail: jmlab1{at}unipv.it.

The kinetic diversity of burst openings responsible for the persistent Na⁺ current (I_NaP) in entorhinal cortex neurons was examined by separately analyzing single bursts. Although remarkable kinetic variability was observed among bursts in terms of intraburst opening probability and mean open and closed times, the values of time constants describing intraburst open times (_o(b)s) and closed times (_c(b)s) were distributed around well-defined peaks. At -40 mV, _o(b) peaks were found at 0.34 (_o(b)1) and 0.77 (_o(b)2) ms, and major _c(b) peaks were found at 0.24 (_c(b)1) and 0.54 (_c(b)2) ms. In 80% of the bursts two preferential gating modes were found that consisted of a combination of either _o(b)1 and _c(b)2 ("intraburst mode 1"), or _o(b)2 and _c(b)1 ("intraburst mode 2"). Individual channels could switch between different gating modalities, but normally tended to maintain a specific gating mode for long periods. Mean burst duration also displayed considerable variability. At least three time constants were found to describe burst duration, and the frequencies at which each of the corresponding "bursting states" occurred varied in different channels. Short-lasting bursting states were preferentially associated with intraburst mode 1, whereas very-long-lasting bursts tended to gate according to mode 2 only or other modes that included considerably longer mean open times. These results show that I_NaP channels can generate multiple intraburst open and closed states and bursting states, but these different kinetic states tend to combine in definite ways to produce a limited number of prevalent, well-defined gating modalities. Modulation of distinct gating modalities in individual Na⁺ channels may be a powerful form of plasticity to influence neuronal excitability and function.

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