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Ionic currents in the guinea-pig taenia coli.

H Inomata, C Y Kao

The Journal of Physiology

|February 1, 1976

Summary

This study reveals that the early inward current in guinea-pig taenia coli is primarily carried by calcium ions (Ca2+), not sodium ions (Na+). This finding clarifies the ionic basis of electrical activity in smooth muscle cells.

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Area of Science:

Electrophysiology
Smooth Muscle Physiology
Ion Channel Function

Background:

The ionic mechanisms underlying electrical activity in smooth muscle, specifically the taenia coli of the guinea-pig, are not fully elucidated.
Previous studies have suggested roles for both sodium and calcium ions in generating membrane currents, but definitive evidence is lacking.

Purpose of the Study:

To investigate the ionic basis of the early transient inward current in guinea-pig taenia coli.
To differentiate the contributions of sodium (Na+) and calcium (Ca2+) ions to this current using voltage-clamp techniques.

Main Methods:

Utilized a double sucrose-gap voltage-clamp technique on short segments of guinea-pig taenia coli.
Manipulated extracellular ion concentrations, including sodium (Na+) and calcium (Ca2+), and employed tetraethylammonium ion (TEA) to block potassium currents.
Measured and analyzed early transient inward currents and late maintained outward currents.

Main Results:

The late outward current was confirmed to be primarily carried by potassium (K+) ions.
The early inward current's reversal potential (Ea) was not significantly affected by reducing extracellular sodium concentration ([Na+]o) or replacing Na+ with other cations.
Reducing extracellular calcium concentration ([Ca2+]o) shifted Ea negatively and reduced the early current, while increasing [Ca2+]o enhanced the early current and its conductance.

Conclusions:

The early inward current in guinea-pig taenia coli is predominantly carried by calcium ion (Ca2+) influx.
Sodium ions (Na+) play a minimal role in the early inward current under the studied conditions.
Calcium ions are the principal charge carriers responsible for the initial depolarization phase in taenia coli smooth muscle.

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