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Membrane potential responses of paramecium caudatum to bitter substances: existence of multiple pathways for bitter
Abstract:
The membrane potential responses of Paramecium caudatum to the external application of bitter substances were examined by employing conventional electrophysiological techniques. Mutant cells defective in voltage-gated Ca2+ channels were used to record the potential responses in the absence of contamination by Ca2+ action potentials. The cells produced a transient depolarization followed by a transient hyperpolarization in response to a rapid whole-cell application of chloroquine, strychnine nitrate or brucine. Of these chemicals, chloroquine was the most potent. Cells produced a simple depolarization in response to a localized application of test chemicals to the anterior region, whereas they produced a transient hyperpolarization in response to an application to the posterior region. Membrane potential responses to an application of chloroquine declined with repeated application. The presence of chloroquine in the external bathing solution strongly inhibited the membrane potential responses to an application of brucine or strychnine. However, the presence of chloroquine did not affect the membrane potential responses to an application of quinine. It is suggested that chloroquine, strychnine and brucine share a common component of their transduction pathways, but that the transduction pathway for quinine is different.
Insights
Paramecium caudatum cells exhibit distinct membrane potential changes when exposed to bitter substances like chloroquine. These responses suggest shared and distinct sensory pathways for different bitter compounds.
Area of Science:
- * Protozoology
- * Electrophysiology
- * Sensory Biology
Background:
- * Paramecium caudatum, a single-celled organism, is known to respond to environmental stimuli.
- * Understanding the sensory mechanisms of protozoa provides insights into basic cellular responses.
- * Bitter substances are known to elicit behavioral responses in various organisms.
Purpose of the Study:
- * To investigate the electrophysiological responses of Paramecium caudatum to bitter substances.
- * To differentiate the signaling pathways of various bitter compounds in Paramecium.
- * To identify potential shared transduction mechanisms for bitter taste perception.
Main Methods:
- * Conventional electrophysiological techniques were used to record membrane potential.
- * Mutant Paramecium cells lacking voltage-gated Ca2+ channels were utilized to isolate responses.
- * Localized and whole-cell application of bitter substances (chloroquine, strychnine, brucine, quinine) were performed.
Main Results:
- * Chloroquine, strychnine, and brucine induced transient depolarization followed by hyperpolarization.
- * Chloroquine was the most potent among the tested bitter substances.
- * Responses varied based on the application site (anterior vs. posterior), and repeated chloroquine application led to diminished responses.
- * Chloroquine inhibited responses to strychnine and brucine, but not quinine, suggesting distinct pathways.
Conclusions:
- * Chloroquine, strychnine, and brucine likely share a common signal transduction pathway in Paramecium.
- * Quinine appears to utilize a different transduction pathway.
- * These findings contribute to understanding the molecular basis of chemosensation in single-celled organisms.