True about gap junctions are all, except -

Ans. is 'c' i.e., Intercellular space 1000 nm o Gap junctions are intercellular connections consist of a pair of hemichannels (connexons) inserted into the membrane of adjacent cells.o Each connexone is made of six identical protein subunits called connexins which enclose a central channel,o When the corresponding connexons of adjacent cell link up end-to-end, they form a continuous channel that permits substances to pass through from cell to cell.o At gap junctions, the intercellular space narrows down to 3nm, thereby helping in binding the cells together.o However, their real physiological significance lies in allowing ions to flow through them, i.e., they conduct ionic current.o This enables electrical excitation to spread from cell to cell, as in smooth and cardiac muscles.o The pore size of gap junctions decreases when intracellular Ca++ is high or pH is low, both of which are commonly associated with cell damage. Closure of gap junctions in response to these stimuli isolates damaged cells so that the Ca+2 and H" do not spread from the damaged to normal cells.