Characterization of the large-conductance Ca-activated K channel in myocytes of rat saphenous artery

We used the patch-clamp method to characterize the BK channel in freshly isolated myocytes from the saphenous branch of the rat femoral artery. Single-channel recordings revealed that the BK channel had a conductance of 187 pS in symmetrical 150 mM KCl, was blocked by external tetraethylammonium (TE...

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Bibliographic Details
Published in:	Pflügers Archiv Vol. 441; no. 2-3; pp. 208 - 218
Main Authors:	Catacuzzeno, L, Pisconti, D A, Harper, A A, Petris, A, Franciolini, F
Format:	Journal Article
Language:	English
Published:	Germany Springer Nature B.V 01-12-2000
Subjects:	Animals Blood Pressure Calcium Calcium - pharmacology Charybdotoxin - pharmacology Electric Conductivity femoral artery Femoral Artery - chemistry Femoral Artery - physiology Kinetics Large-Conductance Calcium-Activated Potassium Channels Male Muscle, Smooth, Vascular - chemistry Muscle, Smooth, Vascular - physiology Patch-Clamp Techniques Polyamines Potassium Channels - drug effects Potassium Channels - physiology Potassium Channels, Calcium-Activated Rats Rats, Wistar Rodents Tetraethylammonium - pharmacology Vascular Resistance
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Summary:	We used the patch-clamp method to characterize the BK channel in freshly isolated myocytes from the saphenous branch of the rat femoral artery. Single-channel recordings revealed that the BK channel had a conductance of 187 pS in symmetrical 150 mM KCl, was blocked by external tetraethylammonium (TEA) with a KD(TEA) of approx. 300 microM at +40 mV, and by submicromolar charybdotoxin (CTX). The sensitivity of the BK channel to Ca was especially high (KD(ca) approx. 0.1 microM at +60 mV) compared to skeletal muscle and neuronal tissues. We also investigated the macroscopic K current, which under certain conditions is essentially sustained by BK channels. This conclusion is based on the findings that the macroscopic current activated upon depolarization follows a single exponential time course and is virtually fully blocked by 100 nM CTX and 5 mM external TEA. We made use of this occurrence to assess the voltage and Ca dependence of the macroscopic BK current. In intact myocytes, the BK channel showed a strong and voltage-dependent reduction of the outward current (62% at +40 mV), most likely due to block by intracellular Ba and polyamines. The results obtained from macroscopic and unitary current indicate that approx. 2.5% of the BK channels are active under physiological conditions, sustaining approx. 20 pA of outward current. Given the high input resistance of these cells, few BK channels are required to open in order to cause a significant membrane hyperpolarization, and thus function to limit the contraction resulting from acute increases in intravascular pressure, or in response to hypertensive pathologies.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	0031-6768 1432-2013
DOI:	10.1007/s004240000414