Electrogenic cation transport across leech caecal epithelium

Area of Science:

• Comparative physiology
• Epithelial transport
• Invertebrate models

Background:

• The leech Hirudo medicinalis possesses a caecal epithelium involved in ion transport.
• Understanding cation transport mechanisms in invertebrates provides insights into fundamental physiological processes.
• The role of the leech caecal epithelium in regulating ion homeostasis is not fully elucidated.

Purpose of the Study:

• To investigate the electrogenic cation transport mechanisms across the caecal epithelium of Hirudo medicinalis.
• To characterize the properties of apical cation uptake and basolateral sodium extrusion.
• To determine the influence of various ions, drugs, and neurotransmitters on transepithelial transport.

Main Methods:

• Utilized modified Ussing chambers to measure transepithelial electrical parameters (resistance, potential difference, short-circuit current).
• Assessed unidirectional sodium transport rates (INa) under various experimental conditions.
• Applied specific ion substitutions, pharmacological agents (amiloride, benzamil, ouabain, DNP), and neurotransmitters to the Ringer solutions.

Main Results:

• The leech caecal epithelium is a 'leaky' epithelium with significant basal short-circuit current (ISC) and sodium transport (INa).
• Apical cation uptake is mediated by non-selective cation conductances, insensitive to amiloride but sensitive to extracellular calcium and trivalent cations.
• Basolateral sodium extrusion involves ouabain-sensitive and -insensitive ATPases, and cyclic AMP (cAMP) stimulates Na+ transport.

Conclusions:

• Electrogenic cation transport in the leech caecal epithelium involves amiloride-insensitive, calcium-sensitive apical uptake and active basolateral extrusion.
• Cyclic AMP plays a role in regulating sodium transport, suggesting a potential signaling pathway.
• Further research is needed to identify the physiological stimulus for cAMP production and its role in leech ion balance.