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(Circulation Research. 2003;93:213.)
© 2003 American Heart Association, Inc.

Cellular Biology

Molecular and Functional Identification of Cyclic AMP-Sensitive BK_Ca Potassium Channels (ZERO Variant) and L-Type Voltage-Dependent Calcium Channels in Single Rat Juxtaglomerular Cells

Ulla G. Friis, Finn Jørgensen, Ditte Andreasen, Boye L. Jensen, Ole Skøtt

From the Department of Physiology and Pharmacology, University of Southern Denmark, Denmark.

Correspondence to Ulla G. Friis, PhD, Physiology and Pharmacology, University of Southern Denmark, Winsloewparken 21, 3., DK-5000 Odense C, Denmark. E-mail ufriis{at}health.sdu.dk

This study aimed at identifying the type and functional significance of potassium channels and voltage-dependent calcium channels (Ca_v) in single rat JG cells using whole-cell patch clamp. Single JG cells displayed outward rectification at positive membrane potentials and limited net currents between -60 and -10 mV. Blockade of K⁺ channels with TEA inhibited 83% of the current at +105 mV. Inhibition of K_V channels with 4-AP inhibited 21% of the current. Blockade of calcium-sensitive voltage-gated K⁺ channels (BK_Ca) with charybdotoxin or iberiotoxin inhibited 89% and 82% of the current, respectively. Double immunofluorescence confirmed the presence of BK_Ca and renin in the same cell. cAMP increased the outward current by 1.6-fold, and this was inhibited by 74% with iberiotoxin. Expression of the cAMP-sensitive splice variant (ZERO) of BK_Ca was confirmed in single-sampled JG cells by RT-PCR. The resting membrane potential of JG cells was -32 mV and activation of BK_Ca with cAMP hyperpolarized cells on average 16 mV, and inhibition with TEA depolarized cells by 17 mV. The cells displayed typical high-voltage activated calcium currents sensitive to the L-type Ca_v blocker calciseptine. RT-PCR analysis and double-immunofluorescence labeling showed coexpression of renin and L-type Ca_v 1.2. The cAMP-mediated increase in exocytosis (measured as membrane capacitance) was inhibited by depolarization to +10 mV, and this inhibitory effect was blocked with calciseptine, whereas K⁺-blockers had no effect. We conclude that JG cells express functional cAMP-sensitive BK_Ca channels (the ZERO splice variant) and voltage-dependent L-type Ca²⁺ channels.

Key Words: BK_Ca • Ca_v • juxtaglomerular cells

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