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Calcium-activated nonselective cationic channel in macula densa cells

³National Institute for Physiological Sciences, Okazaki 444-8585, Japan; ¹Group de Recherche en Transport Membranaire, University of Montreal, Montreal, Quebec H3C 3J7, Canada; and ²Nephrology Research and Training Center, University of Alabama at Birmingham, Birmingham, Alabama 35294

Submitted 30 August 2002 ; accepted in final form 21 April 2003

Patch-clamp experiments in cell-attached (c/a) and inside-out (i/o) configurations were performed to directly observe ionic channels in lateral membranes of macula densa (MD) cells from rabbit kidney. In the presence of 140 mM KCl in the pipette and normal Ringer solution in the bath, we repeatedly observed in c/a and in i/o configurations a 20- to 23-pS channel with a linear current-voltage (I-V) relationship reversing near 0 mV. Ionic replacement in the bath solution clearly indicated a cationic selectivity but with equal permeability for Na⁺ and K+. Single-channel kinetics was characterized by higher open probability at positive membrane potentials. In i/o experiments, elimination of bath Ca²⁺ (1 µM) abolished channel activity in a reversible manner. This MD nonselective cationic channel was found to display a certain Ca²⁺ permeability because single-channel events could be detected when the pipette potential was very negative (–60, –80, and –100 mV) in the presence of 73 mM CaCl₂ in the bath solution. The similarities between this channel and some channels of the transient receptor potential family suggest a possible role for this MD basolateral channel in controlling membrane potential and regulating Ca²⁺ entry during MD cell signaling.

transient receptor potential channels; intracellular calcium; patch clamp; tubuloglomerular feedback; nifedipine

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