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Biophys J, November 2000, p. 2403-2415, Vol. 79, No. 5
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461 USA
Intercellular channels formed by connexins (gap
junctions) are sensitive to the application of transjunctional voltage
(Vj), to which they gate by the separate
actions of their serially arranged hemichannels (Harris, A. L.,
D. C. Spray, and M. V. L. Bennett. 1981. J.
Gen. Physiol. 77:95-117). Single channel studies of both intercellular and conductive hemichannels have demonstrated the existence of two separate gating mechanisms, termed
"Vj-gating" and "loop gating"
(Trexler, E. B., M. V. L. Bennett, T. A. Bargiello, and V. K. Verselis. 1996. Proc. Natl. Acad. Sci.
U.S.A. 93:5836-5841). In Cx32 hemichannels,
Vj-gating occurs at negative
Vj (Oh, S., J. B. Rubin, M. V. L. Bennett, V. K. Verselis, and T. A. Bargiello. 1999. J. Gen. Physiol. 114:339-364; Oh, S.,
C. K. Abrams, V. K. Verselis, and T. A. Bargiello. 2000. J. Gen. Physiol. 116:13-31). A negative charge
substitution at the second amino acid position in the N-terminus
reverses the polarity of Vj-gating of Cx32
hemichannels (Verselis, V. K., C. S. Ginter, and T. A. Bargiello. 1994. Nature. 368:348-351; Oh et al., 2000.
J. Gen. Physiol. 116:13-31). We report that
placement of a negative charge at the 5th, 8th, 9th, or 10th position
can reverse the polarity of Cx32 hemichannel Vj-gating. We conclude that the 1st through
10th amino acid residues lie within the transjunctional electric field
and within the channel pore, as in this position they could sense
changes in Vj and be largely insensitive to
changes in absolute membrane potential (Vm).
Conductive hemichannels formed by Cx32*Cx43E1 containing a negatively
charged residue at either the 8th or 10th position display bi-polar
Vj-gating; that is, the open probability of
hemichannels formed by these connexins is reduced at both positive and
negative potentials and is maximal at intermediate voltages. In
contrast, Cx32*Cx43E1 hemichannels with negative charges at either the
2nd or 5th positions are uni-polar, closing only at positive
Vj. The simplest interpretation of these
data is that the Cx32 hemichannel can adopt at least two different open
conformations. The 1st-5th residues are located within the electric
field in all open channel conformations, while the 8th and 10th
residues lie within the electric field in one conformation and outside
the electric field in the other conformation.
Biophys J, November 2000, p. 2403-2415, Vol. 79, No. 5
© 2000 by the Biophysical Society 0006-3495/00/11/2403/13 $2.00
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