Luminal L-alanine stimulates exocytosis at the K+-conductive epical membrane of Aplysia enterocytes

Jerod Denton, Derek O Boahene, William M. Moran

Research output: Contribution to journalArticle

Abstract

In Aplysia intestine, stimulation of Na+ absorption with luminal adenine increases apical membrane K+ conductance (G(K,a)), which presumably regulates enterocyte volume during stimulated Na+ absorption. However, the mechanism responsible for the sustained increase in plasma membrane K+ conductance is not known for any nutrient-absorbing epithelium. In the present study, we have begun to test the hypothesis that the alanine-induced increase in G(K,a) in Aplysia enterocytes results from exocytic insertion of K+ channels into the apical membrane. We used the fluid-phase marker horseradish peroxidase to assess the effect of alanine on apical membrane exocytosis and conventional microelectrode techniques to assess the effect of alanine on fractional capacitance of the apical membrane (fC(a)). Luminal alanine significantly increased epical membrane exocytosis from 1.04 ± 0.30 to 1.39 ± 0.38 ng·min-1·cm-2. To measure fC(a), we modeled the Aplysia enterocyte as a double resistance-capacitance (RC) electric circuit arranged in series. Several criteria were tested to confirm application of the model to the enterocytes, and all satisfied the model. When added to the luminal surface, alanine significantly increased fC(a) from 0.27 ± 0.02 to 0.33 ± 0.04 (n = 10) after 4 min. There are two possible explanations for our findings: 1) the increase in exocytosis, which adds membrane to the apical plasma membrane, prevents plasma membrane fracture, and 2) the increase in exocytosis delivers K+ channels to the apical membrane by exocytic insertion. After the alanine-induced depolarization of apical membrane potential (V(a)), there is a strong correlation (r = 0.96) between repolarization of V(a), which reflects the increase in G(K,a), and increase in fC(a). This correlation supports the exocytic insertion hypothesis for activation of G(K,a).

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Cell Physiology
Volume275
Issue number5 44-5
StatePublished - 1998
Externally publishedYes

Fingerprint

Aplysia
Enterocytes
Exocytosis
Alanine
Membranes
Capacitance
Cell membranes
Cell Membrane
Electric Capacitance
Microelectrodes
Adenine
Horseradish Peroxidase
Depolarization
Electric Impedance
Membrane Potentials
Intestines
Nutrients
Epithelium
Chemical activation

Keywords

  • Membrane capacitance
  • Nutrient absorption
  • Potassium channels
  • Sea hare

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Cell Biology
  • Physiology
  • Physiology (medical)

Cite this

Luminal L-alanine stimulates exocytosis at the K+-conductive epical membrane of Aplysia enterocytes. / Denton, Jerod; Boahene, Derek O; Moran, William M.

In: American Journal of Physiology - Cell Physiology, Vol. 275, No. 5 44-5, 1998.

Research output: Contribution to journalArticle

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