LOW-CONDUCTANCE INTERCELLULAR COUPLING BETWEEN MOUSE CHROMAFFIN CELLSIN-SITU

1. Patch-clamp experiments were used to compare membrane properties of mouse chromaffin cells in thin tissue slices and of isolated cells in primary culture. The mean membrane input resistance (R-m) and membran e capacitance were 3.1 +/- 0.5 G Omega and 9.1 +/- 0.5 pF in situ and 9.9 +/- 1.8 G Omega and 8.2 +/- 0.2 pF in isolated cells. 2. Spike-lik e currents were observed on top of the calcium currents during depolar izations in thirty out of forty-nine cells in situ. They were not seen in isolated cells nor after addition of Cd2+ (100 mu M) and TTX (10 m u M) to the perfusate of the slices. The mean R-m of cells which displ ayed current spikes (2.3 +/- 0.18 G Omega) was significantly smaller t han that of cells lacking spikes (3.9 +/- 0.25 G Omega). It is suggest ed that the current spikes represent intercellular currents which resu lt from action potential firing in neighbouring cells during the depol arization of the patch-clamped cell. 3. Investigation of capacitative currents induced by square voltage pulses showed a slow component in t wenty-four out of twenty-seven cells in situ. 4. It is concluded that a large fraction of mouse chromaffin cells in situ are electrically co upled. From the slow capacitative currents and the amplitude of the in tercellular current spikes a junctional conductance between chromaffin cells of below 1 nS was deduced. 5. This junctional conductance appea rs to be too lon to support spreading of electrical activity in cases where a single cell is stimulated by an action potential. However, the junctional conductance could allow longer depolarizations of one cell or simultaneous firing of several cells to trigger electrical activit y in neighbouring cells.