Electrophysiological characteristics of the PhoE porin channel from Escherichia coli. Implications for the possible existence of a superfamily of ion channels.

Purified PhoE porins from Escherichia coli were reconstituted in giant proteoliposomes obtained by dehydration-rehydration, and studied by the patch-clamp technique. The following electrophysiological characteristics were observed. (i) The channels for which the probability of opening is maximum around 0 mV, closed at positive and negative potentials, at voltages higher than +/-120 mV. (ii) The channels behaved asymmetrically in response to positive and negative potentials. (iii) The channels exhibited two types of kinetics (fast and slow) on very different time scales. (iv) The channels had several closed states including a reversible inactivated state and a large number of substates. Similar characteristics have been described for channels other than bacterial porins, in particular mitochondrial porins and maxi-chloride channels of the plasma membrane of animal cells. These characteristics might constitute the electrophysiological fingerprint of a superfamily of ion channels for which the basic structure, rather than sequence, would have been conserved during evolution.