Properties of a constitutively active Ca2+-permeable non-selective cation channel in rabbit ear artery myocytes

• Published in: The Journal of physiology Vol. 549; no. 1; pp. 143 - 156
• Main Authors: Albert, A. P., Piper, A. S., Large, W. A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 15.05.2003; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Alkaloids; Animals; Arteries; Benzophenanthridines; Calcium - pharmacokinetics; Cations - metabolism; Diglycerides - pharmacology; Ear, External - blood supply; Enzyme Inhibitors - pharmacology; Ion Channels - physiology; Kinetics; Membrane Potentials - drug effects; Membrane Potentials - physiology; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - physiology; Myocytes, Smooth Muscle - physiology; Original; Patch-Clamp Techniques; Phenanthridines - pharmacology; Protein Kinase C - antagonists & inhibitors; Protein Kinase C - metabolism; Rabbits
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2002.038190

In smooth muscle, non-selective cation conductances contribute to agonist-evoked depolarisation and contraction, and in the present study using patch-pipette techniques we describe the properties of a constitutively active cation channel. With whole-cell recording in K + -free conditions, there was a spontaneous current with a reversal potential ( E r ) that was altered by replacement of external Na + by an impermeant cation, but not when external Cl − was replaced by an impermeant anion. The tonic cation inward current could be carried by Ca 2+ ions and was greatly enhanced when the external Ca 2+ concentration was reduced. In outside-out patches there was spontaneous cation channel activity that could be resolved into three conductance states of about 15, 25 and 40 pS, all with the same E r as the whole-cell current. Kinetic analysis revealed that there were two open times of about 1 and 5 ms and that the currents displayed bursting kinetics with burst durations of approximately 5 ms and 25 ms. Removal of external Ca 2+ ions increased the probability of channel opening ( P o ) sixfold, which was associated with an increase in the longer burst duration. Bath application of the diacylglycerol analogue 1-oleoyl-2-acetyl- sn -glycerol increased P o , but phorbol 12,13-dibutyrate, which stimulates protein kinase C (PKC), reduced channel activity. In contrast, the PKC inhibitor chelerythrine increased the activity of channel currents. It is concluded that in rabbit ear artery myocytes there is a constitutively active Ca 2+ -permeable cation channel that is regulated by external Ca 2+ ions and suppressed by tonic PKC activity. It is proposed that this mechanism may contribute to the resting membrane conductance and basal Ca 2+ influx in this particular arterial preparation.