Cytosolic Ca2+, exocytosis, and endocytosis in single melanotrophs of the rat pituitary.
We have monitored cytosolic [Ca2+] with fura-2 and exocytosis by measuring the membrane capacitance, and we have studied the influence of cytosolic [Ca2+] on secretion in single endocrine cells. As in neurons, cytosolic Ca2+ is sufficient to trigger exocytosis. The rate of secretion grows with the fourth or fifth power of cytosolic [Ca2+], and paired stimuli reveal facilitation. Ca2+ influx through voltage-sensitive Ca2+ channels can stimulate secretion 1000-fold over the basal levels measured biochemically. Unlike neurons, however, melanotrophs continue to secrete for seconds afer a depolarizing pulse, while they extrude or sequester the Ca2+ that has entered through Ca2+ channels. Following episodes of secretion, pituitary cells can retrieve membrane with half-times around 30 s at 32 degrees C, even in the absence of cytosolic K+.
Thomas
P
P
Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle 98195.
Surprenant
A
A
Almers
W
W
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D003600:Cytosol / Q000378:metabolism*; D004594:Electrophysiology; D004705:Endocytosis; D005089:Exocytosis; D009074:Melanocyte-Stimulating Hormones / Q000096:biosynthesis*; D009994:Osmolar Concentration; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D013696:Temperature
D009074:Melanocyte-Stimulating Hormones; D002118:Calcium