BIOPHYSICAL PROPERTIES OF THE HUMAN CARDIAC GAP JUNCTION CHANNEL

1. Gap junction channels interconnect cells of the pacemaking, conduct ion and contraction elements of the heart and also endothelial and smo oth muscle cells of vasculature, thereby providing pathways for electr otonic current spread and for second messenger diffusion. The major ga p junction protein in the cardiovascular system is connexin43. 2. When human connexin43 is stably expressed in pairs of a communication-defi cient cell line (SKHep1) channels are produced with unitary conductanc e (gamma(j) lipophile sensitivity and voltage-dependent gating similar to those of mammalian systems in which connexin43 is endogenously exp ressed. 3. At moderate transjunctional voltages (V(j)), two gamma(j) v alues dominated the recordings, about 60 and 90 pS with CsCl patch sol ution. The smaller channel size is favored by phosphorylating treatmen ts and the larger channel, by dephosphorylating treatments. 4. Human c onnexin43 mutants truncated at the carboxy termini display a change in gamma(j) while a point mutation in the third transmembrane spanning d omain appears to change channel selectivity. 5. Voltage dependence of the human connexin43 channel is marked at V(j)s, above +/-50 mV, but l arge residual conductance remains (due probably to a voltage-insensiti ve substate) even at the largest V(j) values; kinetic but not steady-s tate behavior is affected by phosphorylation state.