Characteristics of two types of calcium channels in rat pituitary gonadotrophs.
The properties of Ca2+ channels in cultured rat pituitary gonadotrophs were analyzed by the patch-clamp technique. The inward Ca2+ currents, recorded in the presence of 5.2 mM Ca2+ or Ba2+, included a fast, transient component with activation-inactivation kinetics and a delayed component with slower activation. The midpoint of the activation curve lay at -30 mV for the transient component and at -12 mV for the delayed component. At the midpoint, changes in potential of 9.5 and 13 mV induced an e-fold change in the activation of the transient and delayed components, respectively. The rate of inactivation of the first component was strongly voltage dependent. At -43 mV, a 7.4-mV change in potential induced an e-fold change in the fraction of Ca2+ channels available to conduct Ca2+ current. During long-lasting (100-200 ms) low-frequency depolarizing voltage-clamp pulses, the size of the delayed component of the Ca2+ current remained constant. The differential effects of membrane potential on inactivation and the different time constants for activation of the two components of the Ca2+ conductance indicate the presence of two types of Ca2+ channels in the membrane of the gonadotroph: the rapidly inactivating current appears to be attributable to a T-type channel, and the noninactivating current corresponds to the L-type channel described in many other cell types.
Stutzin
A
A
Laboratory of Cell Biology and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Stojilković
S S
SS
Catt
K J
KJ
Rojas
E
E
D000818:Animals; D001464:Barium / Q000502:physiology; D001491:Basophils / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D006062:Gonadotropins / Q000378:metabolism*; D006706:Homeostasis; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D013997:Time Factors
D015220:Calcium Channels; D006062:Gonadotropins; D001464:Barium; D002118:Calcium