A Molecular Map of G Protein Alpha Chains in Microdissected Rat Nephron Segments

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Membrane-associated guanine nucleotide binding proteins regulate many receptor-mediated signals. Heterogeneity of biochemical and functional properties in nephron segments could be due to differences in G protein expression. To ascertain whether such heterogeneity of G proteins is present in various nephron segments, this study examines the distribution and relative abundance of G protein alpha chains in microdissected medullary thick ascending limb, cortical collecting tubules, outer medullary collecting tubules, proximal inner medullary tubules, and distal inner medullary tubules. Reverse transcription and polymerase chain reactions were employed using oligonucleotides encoding highly conserved regions of all known alpha chains. The cDNA was sequenced for alpha chain identification. The alphai2 versus alphas distribution was different in the outer medullary collecting tubules, when compared with the medullary thick ascending limb (P < 0.001) or the cortical collecting tubule, the proximal inner medullary tubules, and the distal inner medullary tubules (P < 0.05). These latter four segments did not significantly differ from each other. A similar analysis was applied to the frequently used line of kidney cells, LLC-PK1, whose exact cellular origin remains unclear. Interestingly, we detected both alphai2 and alphai3, while only alphai2 was detected in the rat distal nephron. No alphao or alphaz reverse transcription PCR products were detected. In contrast alpha11 and alpha (14) members of the more recently described alphaq family were detected in the outer medullary collecting tubules and the proximal inner medullary tubules, respectively. We conclude that the majority of nephron segments have a relatively constant distribution of G protein alpha chains. (J. Clin. Invest. 1993. 92:786-790.) Key words: (5)G proteins. microdissected. rat. nephron. PCR

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