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A-type potassium current in retinal arteriolar smooth muscle cells
Mary K McGahon1, Jennine M Dawicki, C Norman Scholfield
1Centre of Vision Sciences, The Queen's University of Belfast, Institute of Clinical Sciences, The Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA, Northern Ireland.
Investigative Ophthalmology & Visual Science
|August 27, 2005
Summary
A-type potassium current is identified as the primary voltage-dependent current in retinal microvascular smooth muscle. This finding suggests its crucial role in regulating vascular tone by suppressing cell excitability and contractility.
Area of Science:
- Physiology
- Cardiovascular Research
- Ion Channel Biology
Background:
- K(+) currents regulate arterial smooth muscle tone by controlling membrane potential and intracellular Ca(2+).
- Understanding specific K(+) currents in retinal microvascular smooth muscle (MVSM) is crucial for elucidating vascular regulation.
Purpose of the Study:
- Identify and characterize the A-type K(+) current in retinal MVSM.
- Investigate the role of this current in modulating MVSM membrane potential and contractility.
Main Methods:
- Whole-cell perforated patch-clamp recordings from MVSM cells in isolated retinal arterioles.
- Enzymatic treatment to remove basal lamina and decouple endothelial cells from MVSM.
- Pharmacological characterization using K(+) channel blockers like Penitrem A and 4-aminopyridine (4-AP).
Main Results:
- A dominant, non-inactivating current was observed, with a rapidly inactivating A-type current revealed upon inhibition with Penitrem A.
- The A-type current was blocked by 4-AP (10 mM), activated at -60 mV, with peak current densities of 29.7 +/- 5.68 pA/pF at +60 mV.
- 4-AP administration caused a 3-4 mV depolarization and triggered minor MVSM cell contractions/relaxations.
Conclusions:
- A-type K(+) current is the predominant voltage-dependent K(+) current in retinal MVSM.
- This current plays a significant physiological role in reducing MVSM cell excitability.
- The A-type current contributes to the suppression of vascular contractility in retinal microvessels.