Modulation of membrane channel currents by gap junction protein mimetic peptides: size matters

Abstract

. Modulation of membrane channel currents by gap junction protein mimetic peptides: size matters. Am J Physiol Cell Physiol 293: C1112-C1119, 2007. First published July 27, 2007; doi:10.1152/ajpcell.00097.2007.-Connexin mimetic peptides are widely used to assess the contribution of nonjunctional connexin channels in several processes, including ATP release. These peptides are derived from various connexin sequences and have been shown to attenuate processes downstream of the putative channel activity. Yet so far, no documentation of effects of peptides on connexin channels has been presented. We tested several connexin and pannexin mimetic peptides and observed attenuation of channel currents that is not compatible with sequence specific actions of the peptides. Connexin mimetic peptides inhibited pannexin channel currents but not the currents of the channel formed by connexins from which the sequence was derived. Pannexin mimetic peptides did inhibit pannexin channel currents but also the channels formed by connexin 46. The same pattern of effects was observed for dye transfer, except that the inhibition levels were more pronounced than for the currents. The channel inhibition by peptides shares commonalities with channel effects of polyethylene glycol (PEG), suggesting a steric block as a mechanism. PEG accessibility is in the size range expected for the pore of innexin gap junction channels, consistent with a functional relatedness of innexin and pannexin channels.

Do not let death do us part: ‘find-me’ signals in communication between dying cells and the phagocytes

“…46 Therefore, it will be interesting to determine whether Panx1 is involved in the release of any other find-me signals that may either cooperate with nucleotides for phagocyte attraction, or alternatively, serve additional functions during cell clearance. In this context, intracellular AMP is also released through the pannexin channels during apoptosis.…”

Currently Used Methods for Identification and Characterization of Hemichannels

“…A large number of publications demonstrate specific effects of some of these peptides on connexin hemichannels by using in parallel scrambled peptide versions, additional hemichannel blockers and/or studies of their effects on connexin-specific expression systems (Braet et al 2003a(Braet et al , 2003bPearson et al 2005;Gomes et al 2005;Eltzschig et al 2006;Takeuchi et al 2006;DeVuyst et al 2006;De Vuyst et al 2007;Retamal et al 2006Retamal et al , 2007bShintani-Ishida et al 2007). However, it was recently reported that some Cx32, Cx43, and Px1 mimetic peptides cause non-specific blockade of hemichannels formed by Px1, Cx46, and a connexin Cx32 chimera carrying the first extracellular loop of Cx43 (Cx32E143) in the oocyte expression system (Wang et al 2007). Because a similar blocking effect was observed with addition of polyethyleneglycol, the authors proposed that mimetic peptides might exert their actions through a steric block.…”

“…Although the existence of hemichannels and their functions in cultured cells is becoming accepted, some controversy regarding the molecular identity of the hemichannels mediating many responses arose with the identification of pannexin-based hemichannels (Spray et al 2006;Wang et al 2007;Harris et al 2007). This issue is even more conflicting, because many studies revealing the presence and function of connexin hemichannels were conducted using non-physiological experimental protocols that include the application of positive transmembrane potentials and exposure to extracellular solutions lacking divalent cations.…”

Alanine substitution scanning of pannexin1 reveals amino acid residues mediating ATP sensitivity

“…Also, the pharmacology of Panx1 channels matches that of ATP release. Almost all compounds that are reported to inhibit non-vesicular ATP release are effective on the Panx1 channel including connexin mimetic peptides and the inhibitor of the organic anion transporter probenecid [15,16]. Finally, the Panx1 channel is controlled by ATP via a negative feedback loop [17].…”