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This Article Full Text Full Text (PDF) All Versions of this Article: 294/4/C893    most recent 00616.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bolívar, J. J. Articles by Galarraga, E. Search for Related Content PubMed PubMed Citation Articles by Bolívar, J. J. Articles by Galarraga, E.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

A hyperpolarization-activated, cyclic nucleotide-gated, (I_h-like) cationic current and HCN gene expression in renal inner medullary collecting duct cells

¹Departamento de Fisiología, Facultad de Medicina, ²Departamento de Biofísica, Instituto de Fisiología Celular, ³Departamento de Microbiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Cuidad de México; and ⁴Posgrado en Ciencias Genómicas, Universidad Autónoma de la Ciudad de México, Ciudad de México, Mexico

Submitted 11 December 2006 ; accepted in final form 11 January 2008

The cation conductancein primary cultures of rat renal inner medullary collecting duct was studied using perforated-patch and conventional whole cell clamp techniques. Hyperpolarizations beyond –60 mV induced a time-dependent inward nonselective cationic current (I_vti) that resembles the well-known hyperpolarization-activated, cyclic nucleotide-gated I_h and I_f currents. I_vti showed a half-maximal activation around –102 mV with a slope factor of 25 mV. It had a higher conductance (but, at its reversal potential, not a higher permeability) for K⁺ than for Na⁺ (gK⁺/gNa⁺ = 1.5), was modulated by cAMP and blocked by external Cd²⁺ (but not Cs⁺ or ZD-7288), and potentiated by a high extracellular K⁺ concentration. We explored the expression of the I_h channel genes (HCN1 to -4) by RT-PCR. The presence of transcripts corresponding to the HCN1, -2, and -4 genes was observed in both the cultured cells and kidney inner medulla. Western blot analysis with HCN2 antibody showed labeling of 90- and 120-kDa proteins in samples from inner medulla and cultured cells. Immunocytochemical analysis of cell cultures and inner medulla showed the presence of HCN immunoreactivity partially colocalized with the Na⁺-K⁺-ATPase at the basolateral membrane of collecting duct cells. This is the first evidence of an I_h-like cationic current and HCN immunoreactivity in either kidney or any other nonexcitable mammalian cells.

kidney; hyperpolarization-activated current; nonselective cation channel; sodium transport