Gap junction channels: distinct voltage-sensitive and -insensitive conductance states.

摘要: All mammalian gap junction channels are sensitive to the voltage difference imposed across junctional membrane, and parameters of sensitivity have been shown vary according protein that is expressed. For connexin43, major in cardiovascular system, uterus, between glial cells brain, clamp studies transjunctional voltages (Vj) exceeding +/- 50 mV reduce conductance (gj). However, substantial gj remains at even very large Vj values; this residual voltage-insensitive has termed gmin. We explored mechanism underlying gmin using several cell types which connexin43 endogenously expressed as well communication-deficient hepatoma transfected with cDNA encoding human connexin43. pairs transfectants exhibiting series resistance-corrected maximal (gmax) values ranging from 90 nS, ratio gmin/gmax was found be relatively constant (about 0.4–0.5), indicating responsible for voltage-sensitive -insensitive components not independent. Single channel further revealed different sizes comprise components, open times larger, more events declined near zero voltages, despite high conclude component ascribable a substate rather than presence multiple membrane. These thus demonstrate certain channels, closure response specific stimuli may graded, all-or-none.