Differential expression of calcium channel subtypes in the bovine adrenal medulla

This study aimed at determining the distribution and expression levels of d ifferent subtypes of Ca2+ channels in the bovine adrenal medulla, and wheth er individual subtypes were more abundant in chromaffin cells exhibiting an adrenergic or a noradrenergic phenotype. In situ hybridization using ribop robes specific for the pore-forming Ca2+ channel alpha (1D) (L-type channel ), alpha (1B) (N-type channel), and alpha (1A) (P/Q-type channel) subunits of bovine chromaffin cells showed a broad distribution of the three transcr ipts in adrenal medulla tissue. However, a tissue-specific expression patte rn of individual subunits was found; whereas alpha (1B) mRNA was homogeneou sly distributed throughout the medulla, alpha (1D) and alpha (1A) transcrip ts were present at higher densities in the internal medullary area, far awa y from the adrenal cortex. These results were corroborated by comparative a nalysis of the alpha (1B), alpha (1D), and alpha (1A) products amplified by RT-PCR from total RNA extracted from small pieces of tissue dissected out from external or internal medullary areas. Interestingly, immunohistochemic al experiments performed in adrenal gland sections, using antidopamine-beta -hydroxylase and anti-phenylethanolamine-N-methyltransferase antibodies, i ndicated a higher density of noradrenergic over adrenergic chromaffin cells in the internal medullary region. These results provide direct evidence in favor of a heterogeneous distribution of Ca2+ channel subtypes in the adre nal medulla, in agreement with previous functional data showing that blocka de of the high K+-elicited responses by dihydropyridines was greater in nor adrenergic than in adrenergic chromaffin cells. These differences may be re levant for the differential release regulation of each catecholamine under physiological and pathophysiological conditions. Copyright (C) 2001 S. Karg er AG, Basel.