Simultaneous monitoring of cellular depolarization and contraction: a new method to investigate excitability and contractility in isolated smooth muscle cells.

The present experiments were performed to establish a method for simultaneous monitoring of excitation and contraction in isolated smooth muscle cells. The smooth muscle cells were dissociated from the colons of Wistar rats by enzymatic digestion. All the experiments were performed on mixtures of circular and longitudinal cells. In a first set of experiments, focal extracellular potentials (FEPs) and transmembrane action potentials (APs) were simultaneously recorded from the cells by use of extracellular and intracellular pipettes, respectively. In a second set of experiments, cellular contraction induced by chemical stimulation was monitored simultaneous with the FEP recordings. The FEPs had spike and plateau amplitudes of 44.5 +/- 2.3 and 8.9 +/- 0.7 mV, respectively, and reproduced the general morphology of gastrointestinal APs. The parallel mechanical measurements from the rat colonic cells showed that they shortened with an average peak contraction of 8.8 +/- 1.4 microm and an average contraction velocity of 8.2 +/- 0.9 microm/s, to develop an average peak force of 1.2 +/- 0.2 microN, and generated an average peak power of 36 +/- 15 pW. Simultaneous monitoring of FEPs and cellular contraction demonstrates correlations between the electrical and mechanical events taking place in the investigated cells.