Adrenergic stimulation of ciliary process epithelium causes surface membrane internalization

Area of Science:

• Ocular physiology
• Cell biology
• Pharmacology

Background:

• Adrenergic stimulation influences ocular physiology.
• The nonpigmented epithelium (NPE) of ciliary processes plays a key role in aqueous humor dynamics.
• Ultrastructural changes in NPE following adrenergic stimulation are not fully understood.

Purpose of the Study:

• To investigate the ultrastructural changes in the nonpigmented epithelium (NPE) of ciliary processes induced by adrenergic stimulation.
• To determine the origin of the intracellular membranous network observed in NPE cells.
• To explore the potential implications of these changes in adrenergic responses.

Main Methods:

• Albino rabbits were topically treated with isoproterenol.
• Electron microscopy was used to examine ultrastructural changes in NPE.
• Cationized ferritin (CF) was employed as an ultrastructural tracer in isolated anterior segments.
• NPE cells were incubated with isoproterenol and CF, with and without timolol maleate pretreatment.

Main Results:

• Isoproterenol induced an extensive intracellular membranous network in NPE cells within 30 minutes.
• Cationized ferritin was found within this network, indicating its origin from the plasma membrane.
• The formation of this network was blocked by timolol maleate, a beta-adrenergic antagonist.
• NPE demonstrated the ability to transport CF from its basilar to apical surface.

Conclusions:

• Adrenergic stimulation triggers rapid internalization of plasma membrane by the NPE.
• This membrane internalization is a beta-adrenergic receptor-mediated process.
• The observed phenomenon may be involved in adrenergic receptor desensitization or regulation of aqueous humor production.