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Characterization of macroscopic outward currents of canine colonic myocytes
1Department of Physiology, University of Nevada School of Medicine, Reno 89557.
Abstract:
Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.
Insights
Researchers identified four outward currents in colonic smooth muscle cells. A calcium-activated potassium current significantly influences the repolarization of electrical slow waves in these cells.
Area of Science:
- Physiology
- Electrophysiology
- Gastroenterology
Background:
- Colonic smooth muscle cells generate electrical activity crucial for gut function.
- Understanding ion channel function is key to explaining smooth muscle cell electrophysiology.
Purpose of the Study:
- To characterize the outward currents in colonic smooth muscle cells.
- To identify the specific ion channels responsible for these currents.
- To elucidate their role in colonic smooth muscle electrical activity.
Main Methods:
- Whole-cell voltage-clamp technique applied to colonic smooth muscle cells.
- Pharmacological agents and varying calcium concentrations used to differentiate current components.
- Analysis of current time courses, voltage dependence, and sensitivities.
Main Results:
- Four distinct outward current components were identified: one time-independent and three time-dependent.
- The time-dependent currents exhibited outward rectification and sensitivity to tetraethylammonium.
- A calcium-activated potassium current, a delayed rectifier current, and spontaneous transient outward currents were characterized.
- Calcium-activated potassium current was modulated by calcium levels and specific blockers/activators.
Conclusions:
- Multiple ion currents contribute to the electrical behavior of colonic smooth muscle cells.
- The calcium-activated potassium current plays a significant role in the repolarization phase of electrical slow waves.
- These findings provide insights into the regulation of colonic motility.
