MOLECULAR CHARACTERIZATION OF RENAL CALCIUM-CHANNEL BETA-SUBUNIT TRANSCRIPTS

An apical, hormone-regulated, calcium entry channel in the distal convoluted tubule and/or connecting tubule (DCT/CNT) is thought to play an important role in controlling renal calcium excretion. We previously identified a gene transcript encoding the pore-forming alpha(1)-subunit of a calcium channel (alpha(1A) or CaCh4) which may be a candidate for such a molecule. The properties of voltage-dependent calcium channels are known to be modulated by their beta-subunits. To identify the accessory beta-subunit of DCT/CNT calcium channels, degenerate primers based on published beta-subunit sequences were used to amplify rat kidney cDNA by the polymerase chain reaction (PCR), and the products were subcloned and sequenced. Alternatively spliced transcripts of three beta-subunit genes (beta(2), beta(3), and beta(4)) were identified. Northern blot analysis indicated that beta 4-subunit is preferentially expressed in kidney cortex. Transcripts of all three beta-subunit genes were detected by PCR in microdissected nephron segments, but only beta 4-subunit was found in DCT/CNT. As the beta(4)- and alpha(1A)-subunits colocalize to the DCT/CNT, we hypothesize that they may be constituent subunits of a renal calcium channel regulated by a hormone(s).