(44) NONELECTROLYTE-REVEALED GEOMETRY OF HIGH AND LOW CONDUCTANCE STATES OF THE MAMMALIAN PORIN CHANNEL, VDAC

O.V. Krasilnikov (1,2), C.M.M. Carneiro (2,3), L.N. Yuldasheva (2), A.C. Campos de Carvalho (3) and R.A. Nogueira (2)
(1) Institute of Physiology and Biophysics, 700095 Tashkent, Uzbekistan
(2) Dept. of Biophysics and Radiobiology, UFPE, 50670-901, Recife, PE, Brazil
(3) Institute of Biophysics Carlos Chagas Filho, UFRJ, Rio de Janeiro, RJ, Brazil

Recently suggested methodology (J. Memb. Biol., 1998, 161(1): 83-92) was applied on the mammalian porin channel (VDAC, Porin-31BM). The channel was reconstituted in planar lipid bilayers under voltage clamp conditions. Filling of the channel with different non-electrolytes through the cis (side of VDAC addition) and through the trans-opening was estimated.

At the high conductance state, the maximal sizes of cis and trans-openings is ~2 nm and ~4 nm in diameter. The trans end of the channel is funnel shaped, diminishing from ~4 nm in diameter at the trans opening, to ~2 nm, approximately 40% at the distance through the channel. The remaining 60%-part of the channel appears cylindrical with a diameter of ~2.0 nm.

At the low conductance "closed" state (induced by 50 mV-application at the cis-side) the cis part of the channel lumen could be also approximated with a cylinder, but with a slightly smaller diameter (~1.8 nm) than for the high conductance state. The trans side continues to appear funnel-shaped with the two sides differing only slightly in diameter: 1.8 nm and 2.4 nm for cis and trans side, respectively.

Assuming that the total length of the channel is equal to 4.6 nm, the calculated change in channel volume was established to be ~9.3 nm3.