AJP - Heart and Circulatory Physiology, Vol 256, Issue 2 455-H459, Copyright © 1989 by American Physiological Society
Pertussis toxin effects on transmitter release from perivascular nerve terminals
M. Nozaki and N. Sperelakis
Department of Physiology and Biophysics, College of Medicine, University of Cincinnati, Ohio 45267-0576.
Pertussis toxin (PT) was used to investigate the possible involvement of an
inhibitory GTP-binding protein (G protein) in neuromuscular transmission at
the sympathetic nerve terminal of guinea pig mesenteric artery. When the
intracellular microelectrode technique was used, the amount of transmitter
released was evaluated by recording the amplitude of excitatory junction
potentials (EJPs) in the vascular smooth muscle (VSM) cells. EJPs were
evoked by perivascular nerve stimulation with brief square pulses. The
amplitude of EJPs was depressed by exogenously applied norepinephrine (NE)
(greater than or equal to 10(-7) M) or histamine (greater than or equal to
10(-7) M). However, these effects of NE and histamine on EJP amplitude were
almost completely blocked in PT-pretreated VSM cells (2 x 10(-7) g/ml PT,
24 h at 21 degrees C). These effects of PT pretreatment were time and
temperature dependent. In contrast, there was no significant change in the
resting membrane potential (-70.1 +/- 2.1 mV) or input resistance (11.9 +/-
0.4 M omega) in the VSM cells after PT pretreatment. These results suggest
that the effects of NE and histamine on EJP amplitude may be mediated by
PT-sensitive G proteins in the presynaptic nerve terminal.
