A voltage-gated K+ current in renal inner medullary collecting duct cells

1 Departamento de Fisiología, Facultad de Medicina, and 2 Departamento de Biofísica, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City DF, 04510, Mexico Submitted 25 February 2003 ; accepted in final form 9 December 2003 We studied the K + -selective conductances in primary cultures of rat renal inner medullary collecting duct (IMCD) using perforated-patch and conventional whole cell techniques. Depolarizations above –20 mV induced a time-dependent outward K + current ( I vto ) similar to a delayed rectifier. I vto showed a half-maximal activation around 5.6 mV with a slope factor of 6.8 mV. Its K + /Na + selectivity ratio was 11.7. It was inhibited by tetraethylammonium, quinidine, 4-aminopyridine, and Ba 2+ and was not Ca 2+ dependent. The delayed rectifying characteristics of I vto prompted us to screen the expression of Kv1 and Kv3 families by RT-PCR. Analysis of RNA isolated from cell cultures revealed the presence of three Kv -subunits (Kv1.1, Kv1.3, and Kv1.6). Western blot analysis with Kv -subunit antibodies for Kv1.1 and Kv1.3 showed labeling of 70-kDa proteins from inner medulla plasmatic and microsome membranes. Immunocytochemical analysis of cell culture and kidney inner medulla showed that Kv1.3 is colocalized with the Na + -K + -ATPase at the basolateral membrane, although it is also in the cytoplasm. This is the first evidence of recording, protein expression, and localization of a voltage-gated Kv1 in the kidney IMCD cells. kidney; Kv1.3; potassium channel; potassium transport; whole cell clamp; immunocytochemistry; confocal microscopy Address for reprint requests and other correspondence: J. J. Bolívar, Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, PO Box 70-250, México City DF, 04510, México (E-mail: jjboliv{at}servidor.unam.mx ).