Effect of calcium on the dissociation of the mature rat heart into individual and paired myocytes: electrical properties of cell pairs.

The dissociation of adult rat heart into individual, functionally intact, calcium-tolerant myocytes requires precise manipulation of extracellular calcium levels. Dissociation of intercellular connections is achieved by lowering extracellular calcium to micromolar levels for a short period. By imposing a very small increment in free calcium activity (from 14 to 17 microM) during this period, we achieve a significant yield of functionally intact pairs of myocytes still joined at the intercalated disc. We obtain fewer intact cells, but many of these are paired end to end. These findings permit us to describe some structural characteristics of intercellular connections between cardiac cells and to report unambiguous measurements of electrotonic coupling and dye transfer between rat cardiac cell pairs. We find that the strength of electrical coupling between cells isolated as pairs with intact junctional contacts is much greater than that measured between cell pairs that have formed new junctional contacts.