AJP - Cell Physiology, Vol 265, Issue 4 C869-C876, Copyright © 1993 by American Physiological Society
Receptor-activated currents in mouse fibroblasts expressing transfected bombesin receptor subtype cDNAs
K. Kusano, H. Gainer, J. F. Battey, Z. Fathi and E. Wada
Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
BALB/c 3T3 cells do not normally express receptors for bombesin-like
peptides [bombesin (Bn), gastrin-releasing peptide (GRP), and neuromedin B
(NmB)]. Transfection of BALB/c 3T3 cells with complementary DNA-encoding
GRP receptors or NmB receptors leads to stable expression of functional GRP
receptors (GRP Rt) or NmB receptors (NmB Rt), respectively, which are
coupled to cell membrane ion channels. Whole cell current analysis using
patch electrodes shows that the activation of these newly expressed
receptors induces cation conductance increases, most frequently a
Ca(2+)-activated plasma membrane K+ conductance. The dose-response
(peak-current) relations of both transfected receptor subtypes were
sigmoidal and exhibited threshold activation concentration in the picomole
range and the saturation of responses to higher concentrations than 10(-8)
M. The GRP Rt responded about equally to GRP, NmB, and Bn when compared at
equimolar levels, despite their known difference in binding affinity for
the three peptides (GRP, Bn > NmB). In contrast, for the NmB Rt, the NmB
was more potent than GRP or Bn. Among four GRP/Bn-receptor antagonists
tested, the [D-Phe6]Bn(6-13) ethyl ester suppressed GRP Rt responses at low
concentrations (10(-7) M). N-acetyl-GRP-(20-26) amide,
[Leu13-psi(CH2NH)-Leu14]Bn, and [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P
also blocked GRP Rt responses but at higher concentrations (10(-5) M).
However, at these concentrations, these four antagonists had little effect
on NmB Rt responses, thereby showing a specificity of these antagonists for
the GRP receptors.
