Calcium in the toad (Bufo marinus) cornea: binding by the stroma

Area of Science:

• Ophthalmology
• Comparative Physiology
• Biochemistry

Background:

• The cornea's ionic composition is crucial for its transparency and function.
• Calcium (Ca) plays vital roles in cellular processes, but its corneal distribution and binding are not fully understood.

Purpose of the Study:

• To investigate the concentration, distribution, and binding characteristics of calcium within the toad (Bufo marinus) cornea.
• To explore the exchangeability and release mechanisms of stromal calcium.

Main Methods:

• Measurement of total calcium concentration in corneal tissues and aqueous humor.
• Use of radioactive 45Ca isotope to assess calcium exchangeability and efflux from the corneal stroma.
• In vitro experiments to determine the effect of various divalent ions on 45Ca efflux.

Main Results:

• Total corneal calcium was 2.6 mmol/kg wet wt, with the stroma containing a significant portion (2.2 mmol/kg wet wt).
• Approximately 80% of total corneal calcium is sequestered or bound, predominantly in the stroma.
• Stromal calcium is highly exchangeable (85-90%) and its efflux is enhanced by Ca2+ and La3+ more than other alkaline earth ions.

Conclusions:

• The amphibian corneal stroma preferentially binds calcium ions at specific sites.
• This specific binding suggests a potential functional role for stromal calcium in corneal physiology.
• Further research is needed to elucidate the precise functional significance of this bound calcium.