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Ionic mechanisms of intestinal electrical control activity.

T Y El-Sharkaway, E E Daniel

The American Journal of Physiology

|November 1, 1975

Summary

Investigating the electrogenic Na pump in rabbit jejunal smooth muscle revealed that electrical control activity (ECA) is not solely dependent on pump oscillations. Ionic environment alterations suggest conductance changes are key.

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Area of Science:

Gastroenterology
Physiology
Electrophysiology

Background:

The electrical control activity (ECA) in intestinal smooth muscle is crucial for regulating motility.
The precise mechanisms underlying ECA generation, particularly the role of the electrogenic Na pump, remain incompletely understood.

Purpose of the Study:

To investigate the role of the electrogenic Na pump and ionic environment in generating electrical control activity (ECA) in rabbit jejunal smooth muscle.
To differentiate between pump-driven oscillations and ion conductance changes as the primary drivers of ECA.

Main Methods:

Studied the effects of electrogenic Na pump inhibition and stimulation on ECA in rabbit jejunal smooth muscle.
Manipulated the ionic environment by altering external Na and Ca concentrations and replacing chloride with various anions.
Utilized electrophysiological techniques to record membrane potential and control potentials (CPs).

Main Results:

Pump inhibition abolished ECA, while stimulation initially hyperpolarized the membrane before CP appearance.
Lowering external Na or withdrawing Ca reversibly abolished ECA; verapamil had no effect.
Chloride replacement transiently augmented CP secondary depolarization and decreased frequency, with initial depolarization largely unaffected.
Nitrate substitution increased CP frequency and spiking activity without altering CP configuration.

Conclusions:

Intestinal ECA likely arises from sequential conductance changes, primarily to Na+ and subsequently to Cl-, rather than solely from oscillatory electrogenic Na pump activity.
The findings challenge the prevailing hypothesis of an oscillatory electrogenic pump as the sole generator of intestinal control potentials.

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