Ca2+ channels in clonal rat anterior pituitary cells (GH3/B6).
In clonal rat somatomammotroph cells (GH3/ B6) Ca2+ influx through voltage-dependent Ca2+ channels is important for regulating the Ca2+ concentration that mediates hormone secretion. To study the Ca2+ channel subtypes in GH3/B6 cells, Ca2+ channel currents were recorded with the whole-cell configuration of the patch-clamp technique using Ba2+ as the charge carrier. Forty-nine percent of the total Ba2+ current amplitude was mediated by a nifedipine-sensitive current (L-type). In addition, three other high-voltage-activated Ca2+ channel current components could be distinguished pharmacologically: 10 nM omega-agatoxin-IVA-sensitive current (22%; P-type), omega-conotoxin-MVIIC-sensitive current (18%; Q-type), and toxin-resistant current (24%). Since omega-conotoxin GVIA (2 microM) had no blocking effect, N-type Ca2+ channels are assumed not to be present in GH3/B6 cells. The T-type Ca2+ channel current was either absent or very small. Different pore-forming alpha1 subunits of Ca2+ channels were found to be expressed in GH3/B6 cells, which could be the molecular correlates of the different Ba2+ current subtypes: alpha1G of T-type, alpha1C, alpha1D and alpha1S of L-type, and alpha1A of P/Q-type current. In addition, transcripts for beta1, beta2 and beta3 subunits were detected. Blockage of L-type channels with 10 microM nifedipine or P/Q-type channels with 10 nM omega-agatoxin MVIIC + 200 nM omega-conotoxin blocked action potential firing in GH3/B6 cells and decreased basal prolactin secretion.
Glassmeier
G
G
Abteilung für Angewandte Physiologie, Institut für Physiologie, Universitätsklinikum Hamburg-Eppendorf, Germany.
Hauber
M
M
Wulfsen
I
I
Weinsberg
F
F
Bauer
C K
CK
Schwarz
J R
JR
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000235:genetics* / Q000378:metabolism*; D019433:Chickenpox Vaccine / Q000493:pharmacokinetics; D002999:Clone Cells; D017931:DNA Primers; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020960:omega-Conotoxins / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D019433:Chickenpox Vaccine; D017931:DNA Primers; D009543:Nifedipine; D011388:Prolactin; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC