Ionic Blockade of the Rat Connexin40 Gap Junction Channel by Large Tetraalkylammonium Ions

Abstract

The rat connexin40 gap junction channel is permeable to monovalent cations including tetramethylammonium and tetraethylammonium ions. Larger tetraalkyammonium (TAA(+)) ions beginning with tetrabutylammonium (TBA(+)) reduced KCl junctional currents disproportionately. Ionic blockade by tetrapentylammonium (TPeA(+)) and tetrahexylammonium (THxA(+)) ions were concentration- and voltage-dependent and occurred only when TAA(+) ions were on the same side as net K(+) efflux across the junction, indicative of block of the ionic permeation pathway. The voltage-dependent dissociation constants (K(m)(V(j))) were lower for THxA(+) than TPeA(+), consistent with steric effects within the pore. The K(m)-V(j) relationships for TPeA(+) and THxA(+) were fit with different reaction rate models for a symmetrical (homotypic) connexin gap junction channel and were described by either a one- or two-site model that assumed each ion traversed the entire V(j) field. Bilateral addition of TPeA(+) ions confirmed a common site of interaction within the pore that possessed identical K(m)(V(j)) values for cis-trans concentrations of TPeA(+) ions as indicated by the modeled I-V relations and rapid channel block that precluded unitary current measurements. The TAA(+) block of K(+) currents and bilateral TPeA(+) interactions did not alter V(j)-gating of Cx40 gap junctions. N-octyl-tributylammonium and -triethylammonium also blocked rCx40 channels with higher affinity and faster kinetics than TBA(+) or TPeA(+), indicative of a hydrophobic site within the pore near the site of block.

Reversible Pore Block of Connexin Channels by Cyclodextrins

“…Voltage-dependent block of Cx40 and Cx43 junctional channels by several tetraalkylammonium ions has been demonstrated (99), as has block of Cx40 junctional channels by the polyanion spermine (100).…”

Biophysical properties of homomeric and heteromultimeric channels formed by cardiac connexins

“…Apparently, one site of interaction within the pore gates so quickly that it precludes recording single channels. This blocking does not interfere with other gating phenomena, like the V j gating of Cx40 [74].…”

Block of Specific Gap Junction Channel Subtypes by 2-Aminoethoxydiphenyl Borate (2-APB)

“…However, only very few drugs have been identified that block gap junction channels, and most of these are nonspecific, acting on other channel types. Among the classes of molecules that have been shown to reduce gap junction conductance are long-chain alcohols (Johnston et al, 1980;Burt and Spray, 1989); volatile anesthetics (Burt and Spray, 1989); glycyrrhetinic acid derivatives (Davidson and Baumgarten, 1988); oleamide (Guan et al, 1997); aminosulfonates (Bevans and Harris, 1999); tetraalkylammonium ions (Musa et al, 2001); arylaminobenzoates (Harks et al, 2001;Srinivas and Spray, 2003); polyamines (Musa and Veenstra, 2003); weak acids, which act by intracellular acidification (Spray et al, 1984); and certain antimalarial compounds, including quinine and derivatives such as mefloquine (Srinivas et al, 2001;Cruikshank et al, 2004). With the exception of intracellular acidification (where apparent pK a s for different connexins vary over a range of approximately 1 pH unit) (Stergiopoulos et al, 1999), polyamines (which blocks connexin (Cx) 40 but not Cx43 channels) (Musa and Veenstra, 2003), and quinine and its derivatives (which potently block Cx50 and Cx36 channels while sparing gap junctions formed of other connexins at even much higher concentrations; Srinivas et al, 2001;Cruikshank et al, 2004), uncoupling agents show poor selectivity for gap junctions formed by different types of connexins.…”