Is sodium necessary for stimulus-secretion coupling in toad (Caudiverbera caudiverbera) adrenal chromaffin cells?
1. Chromaffin cells of the toad were used to investigate the effects of total replacement of extracellular Na+ by monovalent cations or sucrose on secretion of catecholamine (CA). 2. K+, Rb+ or Cs+ in place of Na+ produced an immediate secretory response, which are dependent on extracellular Ca2+ and it was blocked by Co2+. Li+ or choline+ did not affect basal secretion. 3. Isosmotic replacement of Na+ by sucrose caused CA secretion even in the absence of external Ca2+ or in the presence of Ca-channel blockers. 4. Tetraethylammonium decreased the extent of CA release produced by either K+ or Rb+. 5. The secretagogue effect of Na+/K+, Na+/Rb+ or Na+/Cs+ replacement could be explained by a depolarization of the cell membrane, which ultimately will cause Ca2+ influx through voltage-dependent Ca-channels. However, the present results indicate that Na+ may be sufficient but not necessary for CA secretion.
Nassar-Gentina
V
V
Laboratorio de Fisiologia Celular, Facultad de Ciencias, Universidad de Chile, Vina del Mar.
Aguilar
P
P
Luxoro
M
M
D000818:Animals; D001001:Anura / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002586:Cesium / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D002838:Chromaffin System / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D011188:Potassium / Q000502:physiology; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000502:physiology*; D013395:Sucrose / Q000502:physiology
D002395:Catecholamines; D002586:Cesium; D013395:Sucrose; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D002794:Choline; D011188:Potassium