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Journal of Experimental Biology 59,53-65 (1973)
Published by Company of Biologists 1973

Sensory Mechanisms in Paramecium : II. Ionic Basis of the Hyperpolarizing Mechanoreceptor Potential

YUTAKA NAITOH ¹ and ROGER ECKERT ¹

¹ Department of Biology and Brain Research Institute, University of California, Los Angeles, California 90024

1. Small, brief mechanical stimuli were delivered with a microstylus to the surface of Paramecium caudatum bathed in solutions of 1 mM-CaCl₂, 1 mM KCl + 1 mM Tris HCl, pH 7.2.

2. Stimulation of the caudal end produced a graded hyperpolarizing receptor potential which reached a maximum within 50 msec and decayed more slowly.

3. The input conductance at the peak of the caudal receptor potential increased to a value of at least 6 times that of the resting membrane.

4. The potential diminished in amplitude when the membrane was hyperpolarized by injected d.c. current, and reversed sign with sufficient hyperpolarization. The reversal potential in a solution of 1 mM-CaCl₂ + 4 mM-KCl was -37 mV, while the resting potential was -20 mV.

5. The peak of the receptor potential was shifted about + 50 mV per 10-fold increase in extracellular K⁺. Cl^- and Ca²⁺ and other cations produced little or no shift in the potential peak of the response. It is concluded that mechanical stimulation of the caudal surface produces a local increase in conductance, predominantly to K⁺.

6. Extracellular tetraethylammonium converts the normally hyperpolarizing receptor potential to a depolarization similar to the potential produced in response to mechanical stimulation of the anterior surface. The TEA effect is antagonized by calcium ions.

This article has been cited by other articles:

				J. S. McReynolds and A. L. F. Gorman Ionic Basis of Hyperpolarizing Receptor Potential in Scallop Eye: Increase in Permeability to Potassium Ions Science, February 15, 1974; 183(4125): 658 - 659. [Abstract] [PDF]