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Voltage‐gated and agonist‐mediated rises in intracellular Ca2+ in rat clonal pituitary cells (GH3) held under voltage clamp.
Author(s) -
Benham C D
Publication year - 1989
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1989.sp017716
Subject(s) - depolarization , extracellular , biophysics , voltage clamp , chemistry , intracellular , calcium , nifedipine , patch clamp , voltage dependent calcium channel , endocrinology , medicine , membrane potential , electrophysiology , biology , biochemistry
1. Intracellular free calcium (Ca2+i) was estimated in single GH3 cells by dual wavelength emission spectrofluorimetry using the Ca2+ indicator dye Indo‐1, while cells were held under voltage clamp using patch clamp techniques. 2. Depolarization of cells evoked a transient rise in Ca2+i that increased with increasing duration of depolarization to a peak at about 10 s. 3. Calcium transients showed a bell‐shaped dependence on the amplitude of the depolarizing pulse. They were abolished in the absence of extracellular calcium and by application of 10 microM‐nifedipine. 4. Thyrotrophin‐releasing hormone (TRH) evoked a transient rise in Ca2+i that was followed by a more sustained period of elevated Ca2+i in some cells. The transient phase of the response but not the sustained phase was seen in the absence of extracellular calcium. 5. Ca2+i transients evoked by depolarization were not affected by pre‐release of internal Ca2+ stores with TRH. 6. The results demonstrate that voltage‐gated Ca2+ entry and Ca2+ store release can each elevate cytoplasmic free calcium in GH3 cells and may both be important for stimulus‐secretion coupling. Non‐voltage‐gated Ca2+ entry is not a major source of Ca2+ under these conditions.