M. ISOSAKI, T. NAKASHIMA

Department of Pharmacology, Nara Medical University, Kashihara, Nara, Japan


Received January 29, 2001
Accepted November 6, 2001

Summary
We have studied the mechanism of Na+ deprivation-induced catecholamine secretion from freshly isolated bovine adrenal chromaffin cells. Na+ deprivation-induced catecholamine secretion depended on free extracellular Ca2+ concentrations and was almost parallel to 45Ca2+ influx into the cells under various experimental conditions. Furthermore, Na+ deprivation-induced 45Ca2+ influx and catecholamine secretion were actually induced by a relative Na+ concentration gradient across the plasma membrane, but not by simple omission of Na+ from the medium. These results indicate that the deprivation of Na+ from the medium changes the relative Na+ gradient across the plasma membrane and results in Ca2+ influx via a reverse mode of Na+-Ca2+ exchange rather than by inducing Ca2+ entry through Ca2+ channels by eliminating the competition between extracellular Na+ and Ca2+..

Key words
Na⁺-Ca²⁺ exchange · Na+ deprivation · Catecholamine secretion · Adrenal medulla · Chromaffin

Reprint requests
Minoru Isosaki, Department of Pharmacology, Nara Medical University, Kashihara, Nara 634-8521, Japan. Fax: +81-744-25-7657. E-mail: misosaki@naramed-u.ac.jp

ISSN 0862 - 8408