Differences among muscarinic agonists in M1 receptor-mediated nonselective cation channel activation and TASK1 channel inhibition in adrenal medullary cells.

Muscarinic receptor stimulation induces depolarizing inward currents and catecholamine secretion in adrenal medullary (AM) cells from various mammals. In guinea-pig AM cells muscarine and oxotremorine at concentrations ≤ 1 µM produce activation of nonselective cation channels with a similar potency and efficacy, whereas muscarine at higher concentrations produces not only nonselective cation channel activation, but also TASK1 channel inhibition. In rat AM cells, the muscarinic M1 receptor is involved in TASK1 channel inhibition in response to muscarinic agonists, and the efficacy of oxotremorine is half that of muscarine. These pharmacological findings might indicate that different muscarinic receptor subtypes are responsible for the regulation of nonselective cation and TASK1 channel activities. The present study aimed to determine the muscarinic receptor subtypes involved in nonselective cation channel activation in guinea-pig and mouse AM cells. The inward current evoked by 1 µM muscarine was completely suppressed by 100 µM quinine, whereas 30 µM muscarine-induced inward currents were comprised of quinine-sensitive and -insensitive components. The electrophysiological and pharmacological properties of the muscarine-induced currents indicated that the quinine-sensitive and insensitive components are due to nonselective cation channel activation and TASK1 channel inhibition, respectively. Muscarine at 30 µM failed to induce any current in AM cells treated with muscarinic toxin 7 or genetically deleted of the M1 receptor. The KD value of VU0255035 against the muscarinic receptor mediating nonselective cation channel activation was 17.5 nM. These results indicate that the M1 receptor mediates nonselective cation channel activation as well as TASK1 channel inhibition.

PRIMARY CULTURE OF HUMAN FETAL ADRENAL MEDULLARY CELLS / 解剖学报

A simple method for culture of human fetal adrenal medullary cells is described. Enzymatically dissociated human fetal adrenal cells were isolaled by centrifugation on Percoll in the buffer. Adrenal medullary cells with 75%-85% purity were obtained by this procedure. The medullary cells were then plated on plastic culture dishes coated with collagen. After 2-7 days medullary Cells began to flatten and extended processes. A further identification of the cells as medullary in origin was confirmed, by specific catecholamine fluorescence technique. Catecholamine content in the medium was also determined by HPLC.