Ability of repetitive Ca2+ spikes to stimulate prolactin release is frequency dependent.
Measurements of concentrations of cytosolic free Ca2+ ([Ca2+]c) in individual cells has frequently demonstrated periodic transients in [Ca2+]c rather than sustained elevated levels. To determine in anterior pituitary cells if such short and repetitive [Ca2+]c transients stimulated prolactin release, we used a perifusion system with cells loaded with the fluorescent Ca2+-indicator, indo-1. A one second pulse of 100 mM KCl caused an increase in [Ca2+]c with a half peak width of about 18 seconds and an almost coincident increase in prolactin secretion. Subsequent pulses of KCl each caused increases in [Ca2+]c and prolactin release that were the same as the first, up to a pulse frequency of one every two minutes. Increasing the frequency to 1 pulse every minute or 1 pulse every 30 seconds, however, resulted in a serial decline in the amount of prolactin released by each pulse even though each pulse caused a similar peak Ca2+ response. These findings demonstrate that cells become adapted to transient increases in [Ca2+]c of the same magnitude so that they no longer release prolactin if the increases in [Ca2+]c occur frequently enough. Cells may use frequency-encoded Ca2+ signals to stimulate release of prolactin at low frequency to prevent the adaptation that occurs at higher frequencies.
Law
G J
GJ
Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510.
Pachter
J A
JA
Dannies
P S
PS
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D005260:Female; D005456:Fluorescent Dyes; D007211:Indoles; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D015220:Calcium Channels; D005456:Fluorescent Dyes; D007211:Indoles; D011189:Potassium Chloride; D011388:Prolactin; C048960:indo-1; D002118:Calcium