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Published on: July 16, 2013
Identification of a low-threshold T-type calcium channel in bovine ciliary epithelial cells
1Department of Physiology, University of Wales, Cardiff, United Kingdom.
Insights
Researchers identified a low-threshold T-type calcium current in bovine ciliary body cells. This calcium influx occurs at resting membrane potential, crucial for cellular function.
Area of Science:
- Electrophysiology
- Cell Physiology
- Ocular Biology
Background:
- The bovine ciliary body plays a critical role in aqueous humor production and maintaining ocular homeostasis.
- Understanding ion channel function in ciliary body cells is essential for elucidating mechanisms of intraocular pressure regulation.
Purpose of the Study:
- To characterize the inward current in single pigmented cells from the bovine ciliary body.
- To determine the electrophysiological properties and ion selectivity of this inward current.
Main Methods:
- Whole-cell patch-clamp recording technique applied to isolated bovine ciliary body pigmented cells.
- Voltage-clamp analysis to study current activation, inactivation, and voltage dependence.
- Pharmacological profiling using specific ion channel blockers.
Main Results:
- An inward current activated at approximately -75 mV, peaked at -10 mV, and reversed at +40 mV.
- The current exhibited rapid activation and voltage-sensitive inactivation kinetics, with half-maximal inactivation at -88 mV.
- The current was insensitive to tetrodotoxin and nifedipine but partially blocked by Cd2+ and Ni2+.
Conclusions:
- The identified inward current is a low-threshold T-type calcium current.
- Calcium influx through this current occurs at the resting membrane potential, suggesting a significant physiological role.
- These findings contribute to understanding calcium signaling in the ciliary body and its implications for ocular physiology.
Abstract:
The characteristics of an inward current in single pigmented cells from the bovine ciliary body were examined using the whole cell recording technique. The inward current appeared to activate at potentials 30 mV positive to a holding potential of -80 mV, although activation studies revealed that from more negative holding potentials the current activated at about -75 mV, peaked at around -10 mV, and reversed at a potential of +40 mV. The current was small, peak value -72 +/- 24 pA (n = 13), and exhibited rapid activation and slower inactivation kinetics, both processes being voltage sensitive. Inactivation occurred at holding potentials more positive than -120 mV and was complete at -50 mV with a half-maximal membrane potential of -88 mV. The overlap of the inactivation and activation curves between -75 and -50 mV means that, in the steady state, entry of calcium will be greatest in this range and calcium will thus enter the cell at the resting membrane potential. The current was resistant to tetrodotoxin and nifedipine. It was partially blocked by Cd2+ and almost completely blocked by Ni2+. It is concluded that this current is a low-threshold T-type calcium current.
