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. 2007 Apr 27;93(2):483–495. doi: 10.1529/biophysj.106.098517

FIGURE 4.

FIGURE 4

Channel activity in the presence or absence of spermine and unilaterally reduced transjunctional [KCl] gradients. (A) Cx40 channel activity under symmetrical 140 mM [KCl] conditions in the absence of spermine. The activity of zero to three 148 pS channels is evident and the cumulative open probabilites (N × Popen) were identical for each 30-s ±30-mV pulse with an average of 1.02 channels being open for the entire duration of each pulse. (B) The cumulative open probability at +35 mV (6.5 open channels) was reduced by 14% relative to the −35-mV Vj pulse (5.6 open channels) under 75% trans [KCl] conditions in the absence of spermine. The apparent single-channel conductance (γj) was still 144 pS for the cis-side positive and was reduced to 109 pS for the trans-side positive. (C–F). Cx40 channel activity observed during the last 10 s of a 30-s-duration Vj pulse to −35 mV and the first 10 s of the following +35-mV Vj pulse in the presence of 3.5 mM spermine. (C) The γj of the observed channel activity with symmetrical 140 mM [KCl] measured 128 pS in the presence of spermine. This corresponds to a 15% reduction in γj, whereas N × Popen was reduced by 70% during the positive Vj pulse (0.96 relative to 3.14 open channels; +Vj/−Vj) in the presence of 3.5 mM spermine. (D) In this example, the trans side of the gap junction contained only 105 mM KCl. This reduced the apparent trans γj slightly (?20%) to 120 pS but N × Popen declined by 81% (0.42 relative to 2.21 open channels) during the +35-mV Vj step on the cis spermine-containing side of the junction. (E) Results obtained when [KCl] was reduced to 105 mM on the cis 3.5 mM spermine-containing side of the gap junction. N × Popen declined by only 45% (1.13 relative to 2.47 open channels) during the +35-mV step, whereas the apparent γj was reduced by 25% to 90 pS. (F) Cx40 gap junction channel blockade at low (100 μM) [spermine] occurred by a 96% reduction in N × Popen relative to the preceeding −40 mV Vj step (0.24 relative to 3.89 open channels). This dramatic reduction in N × Popen occurred despite the apparently higher γj value of 195 pS on the cis spermine-containing side of the junction due to the electrodiffusion potential established by the asymmetric [KCl] gradient. The dotted line indicates the true zero Ij baseline under these recording conditions (see text for further details).