Electrical Stimulation of Muscle: Field Stimulation
Electrical field stimulation, in which the stimulating current is applied uniformly to the tissue, is useful in several experimental situations. All muscle cells are simultaneously, directly, and nearly equally stimulated. Since each cell is excited without the necessity of propagation, field stimulation ensures that all cells become activated in visceral smooth muscle, despite possible lability of cell-to-cell transmission or decremental propagation, and in normally nonpropagating multiunit smooth muscles. When recording contraction of isolated smooth muscles, field stimulation enables the maximal (for a given set of conditions) isometric developed tension to be recorded because all cells are simultaneously in their active state, and the lack of longitudinal propagation minimizes the passive series elastic element contribution from uncontracted cells in series with contracted cells. Field stimulation is also useful for electromechanical coupling experiments on depolarized smooth muscle; the cells are mechanically activated in a graded fashion without normal action potential generation, as described below. In other types of studies it is also desirable to simultaneously excite or control the membrane potential of all cells. For example, it is necessary for electromechanical coupling experiments on smooth muscle using sucrose-gap voltage-clamp techniques, and for metabolic and O2consumption studies. Electric field techniques also can be used to infer the electrical properties of the junctional membranes (Sperelakis and Hoshiko, 1961; Sperelakis, 1963a; Sperelakis, 1969). In summary, electric field stimulation is advantageous whenever it is necessary to affect all smooth muscle cells simultaneously and equally.
KeywordsElectrical Field Stimulation Field Stimulation Transverse Field Voltage Gradient Longitudinal Field
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