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Gating mechanism of the nuclear pore complex channel in isolated neonatal and adult mouse liver nuclei

R. TONINI^*, F. GROHOVAZ, C. A. M. LAPORTA^* and M. MAZZANTI¹

^* Dipartimento di Fisiologia e Biochimica Generali, I^a Università di Milano,
CNR, Centro di Farmacologia Cellulare e Molecolare e Dibit, Instituto Scientifico San Raffaele, San Raffaele, Italy; and
Dipartimento di Biologia Cellulare e dello Sviluppo, Università `La Sapienza', Roma, Italy

¹Correspondence: Department Biologia Cellulare e dello Sviluppo, Univ. `La Sapienze', piazalle A. Moro, 5, 00185 Roma, Italy.

Several types of ionic channels on the outer membrane of the nuclear envelope communicate with the nuclear cisternae. These are distinct from nucleocytoplasmic pathways, the nuclear pores that span the double membrane of the envelope and are the route for RNA and protein traffic in the nucleus. Recent data indicate that the nuclear pores may also function as ion channels. The most probable candidate for nucleocytoplasmic ion flux is a 300–400 pS pathway observed in many nuclear preparations. Morphological and functional studies of nuclear envelope suggest a tight relationship between the large conductance channel and the pore complex. However, there is no direct evidence for gating of the nuclear pore or its ability to open and close as a conventional channel. This study shows that in liver nuclei isolated from newborn mouse, there is a substantial correspondence between the number of pores and the number of channels recorded during patch-clamp. This is not the case for adult nuclei. Although pore density is comparable, some nuclear cytoskeletal components, such as actin and nonmuscle myosin, show a significant increase in the adult preparation. Previous studies demonstrate the presence of these two proteins in association with the pore complex. Here we show that by using actin filament disrupter, we were able to increase the number of active channels in adult isolated nuclei. We suggest that a functional interaction between actin filaments and the nuclear pore complex could regulate nucleocytoplasmic permeability.—Tonini, R., Grohovaz, F., LaPorta, C. A. M., Mazzanti, M. Gating mechanism of the nuclear pore complex channel in isolated neonatal and adult mouse liver nuclei.

Key Words: NPCs • nuclei isolation • histogram analysis • single-channel currents

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