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1 Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany
2
Department of Physiological Chemistry, Hoppe-Seyler-Strasse 4, D-72076 Tübingen, Germany
3
Department of Anatomy, Medical Faculty, University of Tübingen, Österbergstrasse 3, D-72074 Tübingen, Germany
4
Department of Anatomy, Charité, Philippstrasse 12, D-10098 Berlin
Renin, the key element of the renin–angiotensin–aldosterone system, is mainly produced by and stored in the juxtaglomerular cells in the kidney. These cells are situated in the media of the afferent arteriole close to the vessel pole and can transform into smooth muscle cells and vice versa. In this study, the electrophysiological properties and the molecular identity of the K+ channels responsible for the resting membrane potential (
–60 mV) of the juxtaglomerular cells were examined. In order to increase the number of juxtaglomerular cells, afferent arterioles from NaCl-depleted rats were used, and > 90% of the afferent arterioles were renin positive at the distal end of the arteriole. Whole-cell and cell-attached single-channel patch-clamp experiments showed that juxtaglomerular cells are endowed with a strongly inwardly rectifying K+ channel (Kir). The channel was highly sensitive to inhibition by Ba2+ (inhibition constant 37 µM at 0 mV), but relatively insensitive to Cs+ and, with 142 mM K+ in the pipette, had a single-channel conductance of 31.5 pS. Immunocytochemical studies showed the presence of Kir2.1 but no signal for Kir2.2 in the media of the afferent arteriole. In PCR analyses using isolated juxtaglomerular cells, the mRNA for Kir2.1 and Kir2.2 was detected. Collectively, the results show that Kir2.1 is the dominant component of the channel. The current carried by these channels plays a decisive role in setting the membrane potential of juxtaglomerular cells.
(Received 25 June 2004;
accepted after revision 28 July 2004;
first published online 5 August 2004)
Corresponding author U. Russ: Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany. Email: ulrich.russ{at}uni-tuebingen.de
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