Immunodetection of alpha 1E voltage-gated Ca2+ channel in chromogranin-positive muscle cells of rat heart, and in distal tubules of human kidney

The calcium channel alpha 1E subunit was originally cloned from mammalian b rain. A new splice variant was recently identified in rat islets of Langerh ans and in human kidney by the polymerase chain reaction. The same isoform of alpha 1E was detected in rat and guinea pig heart by amplifying indicati ve cDNA fragments and by immunostaining using peptide-specific antibodies. The apparent molecular size of cardiac alpha 1E was determined by SDS-PAGE and immunoblotting (218 +/- 6 kD; n = 3). Compared to alpha 1E from stably transfected HEK-293 cells, this is smaller by 28 kD. The distribution of al pha 1E in cardiac muscle cells of the conducting system and in the cardiomy oblast cell line H9c2 was compared to the distribution of chromogranin, a m arker of neuroendocrine cells, and to the distribution of atrial natriureti c peptide (ANP). In serial sections from atrial and ventricular regions of rat heart, co-localization of alpha 1E with ANP was detected in atrium and with chromogranin A/B in Purkinje fibers of the conducting system in both r at atrium and ventricle. The kidney is another organ in which natriuretic p eptide hormones are secreted. The detection of alpha 1E in the distal tubul es of human kidney, where urodilatin is stored and secreted, led to the con clusion that the expression of alpha 1E in rat heart and human kidney is li nked to regions with endocrine functions and therefore is involved in the C a2+-dependent secretion of peptide hormones such as ANP and urodilatin.