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Galarraga, E; Bolivar, JJ; Tapia, D; Arenas, G; Castanon-Arreola, M; Torres, H (2008)

A HYPERPOLARIZATION-ACTIVATED, CYCLIC NUCLEOTIDE-GATED, (I-H-LIKE) CATIONIC CURRENT AND HCN GENE EXPRESSION IN RENAL INNER MEDULLARY COLLECTING DUCT C

AM J PHYSIOL-CELL PH 294(4):C893-C906
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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 Ih 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 similar to 90- and similar to 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.