The electrophysiology of single smooth muscle cells isolated from the ctenophoreMnemiopsis

Summary

• 1. Single, giant, smooth muscle cells were isolated enzymatically from longitudinal muscle bundles in the ctenophoreMnemiopsis. The isolation procedure produced fragments of in situ cells and their lengths ranged from 100 μm to several millimeters. The cut ends of the fibers resealed readily and the input impedances of the isolated cells remained high.

• 2. Intracellular recordings were obtained from in situ fibers and used as a baseline to compare with data from isolated cells. In situ fibers had negative resting potentials (−60 mV) and produced fast overshooting action potentials when depolarized. The resting potentials and action potential parameters of the isolated cells were essentially similar.

• 3. Isolated cells were very permeable to Cl⁻ ions but in Cl⁻-free media the resting potential was K⁺ dependent.

• 4. The action potential in the isolated cell could be partially blocked by D-600, verapamil and Cd⁺⁺, implying that there is a Ca⁺⁺ component to the spike. Furthermore, spike amplitude was decreased when external Na⁺ was reduced, suggesting that there is also a Na⁺ dependency.

• 5. Repolarization was achieved by a TEA- and 4-AP-sensitive, K⁺ efflux, part of which passed through Ca⁺-activated channels. The 4-AP sensitive component gave rise to an after-depolarization that may have arisen because of extracellular accumulation of K⁺. Each action potential was associated with a discrete contraction from the fiber and when spike duration was increased, the twitches became very obvious.