Formation of electrical coupling between embryonic Xenopus muscle cells in culture

Electrical coupling between embryonic Xenopus muscle cells in 1-5 day old cultures was studied after isolated cells were manipulated into contact for various periods. The coupling was examined by measuring the electrotonic spread of acetylcholine (ACh)-induced membrane depolarizations or of potential changes induced by intracellular current injection. In 1 day old culture, cells developed coupling rapidly after contact. Strong coupling was observed within 20 min after contact was made. The rate of coupling formation was age dependent. The percentage of cell pairs that established detectable coupling within 30 min of contact decreased from 66% in 1 day culture to 0% in 5 day culture. Older cells, when put into contact for prolonged periods, developed substantial coupling, suggesting that the age of the culture affects the rate of coupling formation rather than the final extent of coupling. Pre-treatment of older cells with colchicine, metabolic inhibitors, Ca2+ and Mg2+-free saline, or trypsin significantly increased the rate of coupling formation to a level close to that of younger cells. This suggests that the reduced rate of coupling was not due to a lack of membrane precursors for the intercellular channels, but was probably due to the appearance of extramembranous constraints for the channel assembly.