AJP - Cell Physiology, Vol 260, Issue 4 C701-C707, Copyright © 1991 by American Physiological Society
Bombesin-like peptides induce Ca2(+)-activated K+ conductance increases in mouse fibroblasts
K. Kusano and H. Gainer
Laboratory of Neurochemistry, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
Peptide receptor-activated membrane currents were studied in two mouse
fibroblast cell lines, Swiss and Balb/c 3T3 cells, using a patch-electrode
voltage-clamp technique. About 50% of the Swiss 3T3 cells examined
responded to bombesin (Bn; 10(-9) to 10(-6) M), either by inducing outward
current flow or inward current flow at the membrane holding potential (Vh)
of -60 mV. The outward current type was more common (approximately 70%)
than the inward current type (30%). The Bn-induced outward current (IBn)
was reversed as the Vh was held to more negative than -90 mV (avg reversal
potential, Erev = -82 mV). This Erev was closer to the equilibrium
potential for K+ and shifted by altering the extracellular-to-intracellular
K+ concentration ratio, in a Nernst-like relationship. The chance of
recording this type of IBn was greatly reduced when K+ conductance blockers
were present in the bathing solution (i.e., tetraethylammonium, Ba2+) or in
the pipette solution (i.e., Cs). It was also reduced by recording with the
pipette containing 5-10 mM ethylene glycol-bis(beta-aminoethyl
ether)-N,N,N',N'-tetraacetic acid. Application of Ca2+ ionophore A23187 (5
microM) induced a similar membrane current with conductance increase. Thus
the outward IBn in Swiss 3T3 cells appears to be induced by the
intracellular Ca2(+)-dependent K+ conductance increase. Applications of
bradykinin (Bk), arginine vasopressin (AVP), neuromedin B (NmB), and
gastrin releasing peptide (GRP) to Swiss 3T3 cells also induced
receptor-activated currents similar to IBn. Balb/c 3T3 cells rarely
generated outward currents in response to Bn, GRP, and NmB but did not
respond to both AVP and Bk with outward current flows.
