Identification of muscarinic receptor subtypes involved in catecholamine secretion in adrenal medullary chromaffin cells by genetic deletion.
OBJECTIVE
Activation of muscarinic receptors results in catecholamine secretion in adrenal chromaffin cells in many mammals, and muscarinic receptors partly mediate synaptic transmission from the splanchnic nerve, at least in guinea pigs. To elucidate the physiological functions of muscarinic receptors in chromaffin cells, it is necessary to identify the muscarinic receptor subtypes involved in excitation.


METHODS
To identify muscarinic receptors, pharmacological tools and strains of mice where one or several muscarinic receptor subtypes were genetically deleted were used. Cellular responses to muscarinic stimulation in isolated chromaffin cells were studied with the patch clamp technique and amperometry.


RESULTS
Muscarinic M₁, M₄ and M₅ receptors were immunologically detected in mouse chromaffin cells, and these receptors disappeared after the appropriate gene deletion. Mouse cells secreted catecholamines in response to muscarinic agonists, angiotensin II and a decrease in external pH. Genetic deletion of M₁, but not M₃, M₄ or M₅, receptors in mice abolished secretion in response to muscarine, but not to other stimuli. The muscarine-induced secretion was suppressed by MT7, a snake peptide toxin specific for M₁ receptors. Similarly, muscarine failed to induce an inward current in the presence of MT7 in mouse and rat chromaffin cells. The binding affinity of VU0255035 for the inhibition of muscarine-induced currents agreed with that for the M₁ receptor.


CONCLUSIONS
Based upon the effects of genetic deletion of muscarinic receptors and MT7, it is concluded that the M₁ receptor alone is responsible for muscarine-induced catecholamine secretion.
Department of Cell and Systems Physiology, University of Occupational and Environmental Health School of Medicine, Kitakyushu, Japan.
Keita
K
Harada
Hidetada
H
Matsuoka
Hironori
H
Miyata
Minoru
M
Matsui
Masumi
M
Inoue
D000313:Adrenal Medulla / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D017353:Gene Deletion; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009116:Muscarine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016716:PC12 Cells; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000494:pharmacology; D013830:Thiadiazoles / Q000494:pharmacology
D002395:Catecholamines; C542801:N-(3-oxo-3-(4-(pyridin-4-yl)piperazin-1-yl)propyl)benzo(c)(1,2,5)thiadiazole-4-sulfonamide; D011976:Receptors, Muscarinic; D013449:Sulfonamides; D013830:Thiadiazoles; D009116:Muscarine